Move thread-local store for WebThreads to Platform.

This CL moves the thread-local storage for Blink threads currently
stored in content::BlinkPlatformImpl to Platform, so that //content's
dependency to WebThread could be reduced further.

The responsibility of creating a physical thread (i.e. base::Thread)
is now shifted to Platform::CreateThread(). Platform also manages
the thread-local storage of WebThreads, making it possible for Platform
to implement CurrentThread() itself.

Platform::CreateThread() and CurrentThread() are no longer virtual;
now they are concrete functions implemented in Platform. It's a bit
unfortunate to have a fat implementation in Platform like this,
because Platform should be a pure interface to embedders. Eventually
we would like to move them to somewhere in platform/.

Bug: 826203
Change-Id: I4406c2f964f0e41e59ef367269b000e81eeb53aa
Reviewed-on: https://chromium-review.googlesource.com/1238094
Commit-Queue: Yuta Kitamura <yutak@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594221}

content/child/blink_platform_impl.cc

@@ -23,10 +23,7 @@
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/lock.h"
-#include "base/synchronization/waitable_event.h"
 #include "base/sys_info.h"
-#include "base/threading/platform_thread.h"
-#include "base/threading/thread.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "base/trace_event/memory_allocator_dump_guid.h"
@@ -359,57 +356,9 @@ BlinkPlatformImpl::BlinkPlatformImpl(
     : main_thread_task_runner_(std::move(main_thread_task_runner)),
       io_thread_task_runner_(std::move(io_thread_task_runner)) {}
 
-void BlinkPlatformImpl::WaitUntilWebThreadTLSUpdate(
-    blink::scheduler::WebThreadBase* thread) {
-  base::WaitableEvent event(base::WaitableEvent::ResetPolicy::AUTOMATIC,
-                            base::WaitableEvent::InitialState::NOT_SIGNALED);
-  thread->GetTaskRunner()->PostTask(
-      FROM_HERE,
-      base::BindOnce(&BlinkPlatformImpl::UpdateWebThreadTLS,
-                     base::Unretained(this), base::Unretained(thread),
-                     base::Unretained(&event)));
-  event.Wait();
-}
-
-void BlinkPlatformImpl::UpdateWebThreadTLS(blink::WebThread* thread,
-                                           base::WaitableEvent* event) {
-  DCHECK(!current_thread_slot_.Get());
-  current_thread_slot_.Set(thread);
-  event->Signal();
-}
-
 BlinkPlatformImpl::~BlinkPlatformImpl() {
 }
 
-std::unique_ptr<blink::WebThread> BlinkPlatformImpl::CreateThread(
-    const blink::WebThreadCreationParams& params) {
-  std::unique_ptr<blink::scheduler::WebThreadBase> thread =
-      blink::scheduler::WebThreadBase::CreateWorkerThread(params);
-  thread->Init();
-  WaitUntilWebThreadTLSUpdate(thread.get());
-  return std::move(thread);
-}
-
-std::unique_ptr<blink::WebThread> BlinkPlatformImpl::CreateWebAudioThread() {
-  blink::WebThreadCreationParams params(blink::WebThreadType::kWebAudioThread);
-  // WebAudio uses a thread with |DISPLAY| priority to avoid glitch when the
-  // system is under the high pressure. Note that the main browser thread also
-  // runs with same priority. (see: crbug.com/734539)
-  params.thread_options.priority = base::ThreadPriority::DISPLAY;
-
-  std::unique_ptr<blink::scheduler::WebThreadBase> thread =
-      blink::scheduler::WebThreadBase::CreateWorkerThread(params);
-  thread->Init();
-  WaitUntilWebThreadTLSUpdate(thread.get());
-  return std::move(thread);
-}
-
-blink::WebThread* BlinkPlatformImpl::CurrentThread() {
-  // TODO(yutak): This only works on non-main threads. We can support
-  // the main thread here as well.
-  return static_cast<blink::WebThread*>(current_thread_slot_.Get());
-}
-
 void BlinkPlatformImpl::RecordAction(const blink::UserMetricsAction& name) {
   if (ChildThread* child_thread = ChildThread::Get())
     child_thread->RecordComputedAction(name.Action());
@@ -757,11 +706,6 @@ bool BlinkPlatformImpl::IsLowEndDevice() {
   return base::SysInfo::IsLowEndDevice();
 }
 
-bool BlinkPlatformImpl::IsMainThread() const {
-  return main_thread_task_runner_.get() &&
-         main_thread_task_runner_->BelongsToCurrentThread();
-}
-
 WebString BlinkPlatformImpl::DomCodeStringFromEnum(int dom_code) {
   return WebString::FromUTF8(ui::KeycodeConverter::DomCodeToCodeString(
       static_cast<ui::DomCode>(dom_code)));

content/child/blink_platform_impl.h

@@ -10,7 +10,6 @@
 
 #include "base/compiler_specific.h"
 #include "base/single_thread_task_runner.h"
-#include "base/threading/thread_local_storage.h"
 #include "base/timer/timer.h"
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
@@ -33,16 +32,6 @@
 #include "content/child/webthemeengine_impl_android.h"
 #endif
 
-namespace base {
-class WaitableEvent;
-}
-
-namespace blink {
-namespace scheduler {
-class WebThreadBase;
-}
-}
-
 namespace content {
 
 class WebCryptoImpl;
@@ -72,10 +61,6 @@ class CONTENT_EXPORT BlinkPlatformImpl : public blink::Platform {
 
   size_t MaxDecodedImageBytes() override;
   bool IsLowEndDevice() override;
-  std::unique_ptr<blink::WebThread> CreateThread(
-      const blink::WebThreadCreationParams& params) override;
-  std::unique_ptr<blink::WebThread> CreateWebAudioThread() override;
-  blink::WebThread* CurrentThread() override;
   void RecordAction(const blink::UserMetricsAction&) override;
 
   blink::WebData GetDataResource(const char* name) override;
@@ -100,22 +85,14 @@ class CONTENT_EXPORT BlinkPlatformImpl : public blink::Platform {
   int DomKeyEnumFromString(const blink::WebString& key_string) override;
   bool IsDomKeyForModifier(int dom_key) override;
 
-  void WaitUntilWebThreadTLSUpdate(blink::scheduler::WebThreadBase* thread);
-
   scoped_refptr<base::SingleThreadTaskRunner> GetIOTaskRunner() const override;
   std::unique_ptr<NestedMessageLoopRunner> CreateNestedMessageLoopRunner()
       const override;
 
- protected:
-  bool IsMainThread() const;
-
  private:
-  void UpdateWebThreadTLS(blink::WebThread* thread, base::WaitableEvent* event);
-
   scoped_refptr<base::SingleThreadTaskRunner> main_thread_task_runner_;
   scoped_refptr<base::SingleThreadTaskRunner> io_thread_task_runner_;
   WebThemeEngineImpl native_theme_engine_;
-  base::ThreadLocalStorage::Slot current_thread_slot_;
   webcrypto::WebCryptoImpl web_crypto_;
   media::WebMediaCapabilitiesClientImpl media_capabilities_client_;
 };

content/ppapi_plugin/ppapi_blink_platform_impl.cc

@@ -164,12 +164,6 @@ void PpapiBlinkPlatformImpl::Shutdown() {
 #endif
 }
 
-blink::WebThread* PpapiBlinkPlatformImpl::CurrentThread() {
-  if (IsMainThread())
-    return main_thread_;
-  return BlinkPlatformImpl::CurrentThread();
-}
-
 blink::WebSandboxSupport* PpapiBlinkPlatformImpl::GetSandboxSupport() {
 #if !defined(OS_ANDROID) && !defined(OS_WIN)
   return sandbox_support_.get();

content/ppapi_plugin/ppapi_blink_platform_impl.h

@@ -29,7 +29,6 @@ class PpapiBlinkPlatformImpl : public BlinkPlatformImpl {
   void Shutdown();
 
   // BlinkPlatformImpl methods:
-  blink::WebThread* CurrentThread() override;
   blink::WebSandboxSupport* GetSandboxSupport() override;
   unsigned long long VisitedLinkHash(const char* canonical_url,
                                      size_t length) override;

content/renderer/renderer_blink_platform_impl.cc

@@ -381,15 +381,12 @@ RendererBlinkPlatformImpl::CreateNetworkURLLoaderFactory() {
 
 void RendererBlinkPlatformImpl::SetCompositorThread(
     blink::scheduler::WebThreadBase* compositor_thread) {
+  // TODO(yutak): Compositor thread is currently owned by RenderThreadImpl,
+  // but should probably be owned by Platform so this wouldn't depend on
+  // WebThread.
   compositor_thread_ = compositor_thread;
   if (compositor_thread_)
-    WaitUntilWebThreadTLSUpdate(compositor_thread_);
-}
-
-blink::WebThread* RendererBlinkPlatformImpl::CurrentThread() {
-  if (main_thread_->IsCurrentThread())
-    return main_thread_.get();
-  return BlinkPlatformImpl::CurrentThread();
+    RegisterExtraThreadToTLS(compositor_thread_);
 }
 
 blink::BlameContext* RendererBlinkPlatformImpl::GetTopLevelBlameContext() {

content/renderer/renderer_blink_platform_impl.h

@@ -197,7 +197,6 @@ class CONTENT_EXPORT RendererBlinkPlatformImpl : public BlinkPlatformImpl {
   blink::WebString ConvertIDNToUnicode(const blink::WebString& host) override;
   service_manager::Connector* GetConnector() override;
   blink::InterfaceProvider* GetInterfaceProvider() override;
-  blink::WebThread* CurrentThread() override;
   blink::BlameContext* GetTopLevelBlameContext() override;
   void RecordRappor(const char* metric,
                     const blink::WebString& sample) override;

content/test/test_blink_web_unit_test_support.cc

@@ -301,12 +301,6 @@ TestBlinkWebUnitTestSupport::GetURLLoaderMockFactory() {
   return url_loader_factory_.get();
 }
 
-blink::WebThread* TestBlinkWebUnitTestSupport::CurrentThread() {
-  if (main_thread_->IsCurrentThread())
-    return main_thread_;
-  return BlinkPlatformImpl::CurrentThread();
-}
-
 bool TestBlinkWebUnitTestSupport::IsThreadedAnimationEnabled() {
   return threaded_animation_;
 }

content/test/test_blink_web_unit_test_support.h

@@ -53,8 +53,6 @@ class TestBlinkWebUnitTestSupport : public BlinkPlatformImpl {
 
   blink::WebURLLoaderMockFactory* GetURLLoaderMockFactory() override;
 
-  blink::WebThread* CurrentThread() override;
-
   bool IsThreadedAnimationEnabled() override;
 
   std::unique_ptr<blink::WebRTCCertificateGenerator>

third_party/blink/public/platform/platform.h

@@ -424,20 +424,24 @@ class BLINK_PLATFORM_EXPORT Platform {
 
   // Threads -------------------------------------------------------
 
-  // Creates an embedder-defined thread.
-  virtual std::unique_ptr<WebThread> CreateThread(
-      const WebThreadCreationParams&);
+  // Thread creation is no longer customizable in Platform. CreateThread()
+  // always creates a new physical thread for Blink. Platform maintains
+  // the thread-local storage containing each WebThread object, so that
+  // CurrentThread() could return the correct thread object.
+  //
+  // TODO(yutak): These non-virtual functions should be moved to somewhere
+  // else, because they no longer require embedder's implementation.
+
+  // Creates a new thread. This may be called from a non-main thread (e.g.
+  // nested Web workers).
+  std::unique_ptr<WebThread> CreateThread(const WebThreadCreationParams&);
 
   // Creates a WebAudio-specific thread with the elevated priority. Do NOT use
   // for any other purpose.
-  virtual std::unique_ptr<WebThread> CreateWebAudioThread();
+  std::unique_ptr<WebThread> CreateWebAudioThread();
 
   // Returns an interface to the current thread.
-  //
-  // The default implementation only works on the main thread. If your
-  // application supports multi-thread, you *must* override this function
-  // as well as CreateThread().
-  virtual WebThread* CurrentThread();
+  WebThread* CurrentThread();
 
   // Returns a blame context for attributing top-level work which does not
   // belong to a particular frame scope.
@@ -744,11 +748,16 @@ class BLINK_PLATFORM_EXPORT Platform {
   virtual bool IsTakingV8ContextSnapshot() { return false; }
 
  protected:
+  void RegisterExtraThreadToTLS(WebThread*);
+
   WebThread* main_thread_;
 
  private:
   static void InitializeCommon(Platform* platform);
 
+  void WaitUntilWebThreadTLSUpdate(WebThread*);
+  void UpdateWebThreadTLS(WebThread* thread, base::WaitableEvent* event);
+
   // Platform owns the main thread in most cases. The pointer value is the same
   // as main_thread_ if this variable is non-null.
   //
@@ -756,6 +765,11 @@ class BLINK_PLATFORM_EXPORT Platform {
   // overrides the old Platform. In this case, main_thread_ points to the old
   // Platform's main thread. See testing_platform_support.h for this.
   std::unique_ptr<WebThread> owned_main_thread_;
+
+  // We can't use WTF stuff here. Ultimately these should go away (see comments
+  // near CreateThread()), though.
+  base::ThreadLocalStorage::Slot current_thread_slot_;
+  base::Lock create_thread_lock_;
 };
 
 }  // namespace blink

third_party/blink/public/platform/scheduler/child/webthread_base.h

@@ -29,8 +29,10 @@ class BLINK_PLATFORM_EXPORT WebThreadBase : public WebThread {
  public:
   ~WebThreadBase() override;
 
+  // CreateWorkerThread() may be called from a non-main thread.
   static std::unique_ptr<WebThreadBase> CreateWorkerThread(
       const WebThreadCreationParams& params);
+
   static std::unique_ptr<WebThreadBase> CreateCompositorThread(
       const WebThreadCreationParams& params);
 

third_party/blink/renderer/modules/animationworklet/animation_worklet_thread_test.cc

@@ -28,7 +28,6 @@
 #include "third_party/blink/renderer/platform/cross_thread_functional.h"
 #include "third_party/blink/renderer/platform/loader/fetch/access_control_status.h"
 #include "third_party/blink/renderer/platform/loader/fetch/resource_loader_options.h"
-#include "third_party/blink/renderer/platform/testing/testing_platform_support.h"
 #include "third_party/blink/renderer/platform/testing/unit_test_helpers.h"
 #include "third_party/blink/renderer/platform/waitable_event.h"
 #include "third_party/blink/renderer/platform/web_thread_supporting_gc.h"
@@ -37,17 +36,6 @@
 namespace blink {
 namespace {
 
-class AnimationWorkletTestPlatform : public TestingPlatformSupport {
- public:
-  // Need to override the thread creating support so we can actually run
-  // Animation Worklet code that would go on a backing thread in non-test
-  // code. i.e. most tests remove the extra threads, but we need this one.
-  std::unique_ptr<WebThread> CreateThread(
-      const blink::WebThreadCreationParams& params) override {
-    return old_platform_->CreateThread(params);
-  }
-};
-
 class TestAnimationWorkletProxyClient : public AnimationWorkletProxyClient {
  public:
   TestAnimationWorkletProxyClient()
@@ -127,7 +115,6 @@ class AnimationWorkletThreadTest : public PageTestBase {
   }
 
   std::unique_ptr<WorkerReportingProxy> reporting_proxy_;
-  ScopedTestingPlatformSupport<AnimationWorkletTestPlatform> platform_;
 };
 
 TEST_F(AnimationWorkletThreadTest, Basic) {

third_party/blink/renderer/modules/webaudio/audio_context_autoplay_test.cc

@@ -84,11 +84,6 @@ class AudioContextAutoplayTestPlatform : public TestingPlatformSupport {
         AudioHardwareSampleRate(), AudioHardwareBufferSize());
   }
 
-  std::unique_ptr<WebThread> CreateThread(
-      const WebThreadCreationParams& params) override {
-    return old_platform_->CreateThread(params);
-  }
-
   double AudioHardwareSampleRate() override { return 44100; }
   size_t AudioHardwareBufferSize() override { return 128; }
 };

third_party/blink/renderer/modules/webaudio/audio_context_test.cc

@@ -72,11 +72,6 @@ class AudioContextTestPlatform : public TestingPlatformSupport {
         AudioHardwareSampleRate(), buffer_size);
   }
 
-  std::unique_ptr<WebThread> CreateThread(
-      const WebThreadCreationParams& params) override {
-    return old_platform_->CreateThread(params);
-  }
-
   double AudioHardwareSampleRate() override { return 44100; }
   size_t AudioHardwareBufferSize() override { return 128; }
 };

third_party/blink/renderer/platform/exported/platform.cc

@@ -33,12 +33,14 @@
 #include <memory>
 
 #include "base/single_thread_task_runner.h"
+#include "base/synchronization/waitable_event.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/memory_dump_manager.h"
 #include "services/service_manager/public/cpp/connector.h"
 #include "services/service_manager/public/cpp/interface_provider.h"
 #include "third_party/blink/public/platform/interface_provider.h"
 #include "third_party/blink/public/platform/modules/webmidi/web_midi_accessor.h"
+#include "third_party/blink/public/platform/scheduler/child/webthread_base.h"
 #include "third_party/blink/public/platform/scheduler/web_thread_scheduler.h"
 #include "third_party/blink/public/platform/web_canvas_capture_handler.h"
 #include "third_party/blink/public/platform/web_graphics_context_3d_provider.h"
@@ -51,6 +53,7 @@
 #include "third_party/blink/public/platform/web_storage_namespace.h"
 #include "third_party/blink/public/platform/web_thread.h"
 #include "third_party/blink/public/platform/websocket_handshake_throttle.h"
+#include "third_party/blink/renderer/platform/cross_thread_functional.h"
 #include "third_party/blink/renderer/platform/font_family_names.h"
 #include "third_party/blink/renderer/platform/fonts/font_cache_memory_dump_provider.h"
 #include "third_party/blink/renderer/platform/heap/blink_gc_memory_dump_provider.h"
@@ -170,6 +173,8 @@ void Platform::Initialize(
   g_platform = platform;
   g_platform->owned_main_thread_ = main_thread_scheduler->CreateMainThread();
   g_platform->main_thread_ = g_platform->owned_main_thread_.get();
+  DCHECK(!g_platform->current_thread_slot_.Get());
+  g_platform->current_thread_slot_.Set(g_platform->main_thread_);
   InitializeCommon(platform);
 }
 
@@ -179,6 +184,8 @@ void Platform::CreateMainThreadAndInitialize(Platform* platform) {
   g_platform = platform;
   g_platform->owned_main_thread_ = std::make_unique<SimpleMainThread>();
   g_platform->main_thread_ = g_platform->owned_main_thread_.get();
+  DCHECK(!g_platform->current_thread_slot_.Get());
+  g_platform->current_thread_slot_.Set(g_platform->main_thread_);
   InitializeCommon(platform);
 }
 
@@ -240,6 +247,12 @@ void Platform::SetCurrentPlatformForTesting(Platform* platform) {
     platform->main_thread_ = platform->owned_main_thread_.get();
   }
 
+  // Set only the main thread to TLS for the new platform. This is OK for the
+  // testing purposes. The TLS slot may already be set when
+  // ScopedTestingPlatformSupport tries to revert to the old platform.
+  if (!platform->current_thread_slot_.Get())
+    platform->current_thread_slot_.Set(platform->main_thread_);
+
   g_platform = platform;
 }
 
@@ -266,9 +279,7 @@ WebThread* Platform::MainThread() const {
 }
 
 WebThread* Platform::CurrentThread() {
-  DCHECK(main_thread_);
-  DCHECK(WTF::IsMainThread());
-  return main_thread_;
+  return static_cast<WebThread*>(current_thread_slot_.Get());
 }
 
 service_manager::Connector* Platform::GetConnector() {
@@ -296,11 +307,43 @@ std::unique_ptr<WebStorageNamespace> Platform::CreateSessionStorageNamespace(
 
 std::unique_ptr<WebThread> Platform::CreateThread(
     const WebThreadCreationParams& params) {
-  return nullptr;
+  std::unique_ptr<scheduler::WebThreadBase> thread =
+      scheduler::WebThreadBase::CreateWorkerThread(params);
+  thread->Init();
+  WaitUntilWebThreadTLSUpdate(thread.get());
+  return std::move(thread);
 }
 
 std::unique_ptr<WebThread> Platform::CreateWebAudioThread() {
-  return nullptr;
+  WebThreadCreationParams params(WebThreadType::kWebAudioThread);
+  // WebAudio uses a thread with |DISPLAY| priority to avoid glitch when the
+  // system is under the high pressure. Note that the main browser thread also
+  // runs with same priority. (see: crbug.com/734539)
+  params.thread_options.priority = base::ThreadPriority::DISPLAY;
+  return CreateThread(params);
+}
+
+void Platform::WaitUntilWebThreadTLSUpdate(WebThread* thread) {
+  base::WaitableEvent event(base::WaitableEvent::ResetPolicy::AUTOMATIC,
+                            base::WaitableEvent::InitialState::NOT_SIGNALED);
+  // This cross-thread posting is guaranteed to be safe.
+  PostCrossThreadTask(*thread->GetTaskRunner(), FROM_HERE,
+                      CrossThreadBind(&Platform::UpdateWebThreadTLS,
+                                      WTF::CrossThreadUnretained(this),
+                                      WTF::CrossThreadUnretained(thread),
+                                      WTF::CrossThreadUnretained(&event)));
+  event.Wait();
+}
+
+void Platform::UpdateWebThreadTLS(WebThread* thread,
+                                  base::WaitableEvent* event) {
+  DCHECK(!current_thread_slot_.Get());
+  current_thread_slot_.Set(thread);
+  event->Signal();
+}
+
+void Platform::RegisterExtraThreadToTLS(WebThread* thread) {
+  WaitUntilWebThreadTLSUpdate(thread);
 }
 
 std::unique_ptr<WebGraphicsContext3DProvider>

third_party/blink/renderer/platform/testing/testing_platform_support.cc

@@ -108,10 +108,6 @@ WebString TestingPlatformSupport::DefaultLocale() {
   return WebString::FromUTF8("en-US");
 }
 
-WebThread* TestingPlatformSupport::CurrentThread() {
-  return old_platform_ ? old_platform_->CurrentThread() : nullptr;
-}
-
 WebBlobRegistry* TestingPlatformSupport::GetBlobRegistry() {
   return old_platform_ ? old_platform_->GetBlobRegistry() : nullptr;
 }

third_party/blink/renderer/platform/testing/testing_platform_support.h

@@ -48,7 +48,6 @@ class TestDiscardableMemoryAllocator;
 }
 
 namespace blink {
-class WebThread;
 
 // A base class to override Platform methods for testing.  You can override the
 // behavior by subclassing TestingPlatformSupport or using
@@ -61,7 +60,6 @@ class TestingPlatformSupport : public Platform {
 
   // Platform:
   WebString DefaultLocale() override;
-  WebThread* CurrentThread() override;
   WebBlobRegistry* GetBlobRegistry() override;
   std::unique_ptr<WebIDBFactory> CreateIdbFactory() override;
   WebURLLoaderMockFactory* GetURLLoaderMockFactory() override;

third_party/blink/renderer/platform/testing/testing_platform_support_with_custom_scheduler.cc

@@ -29,16 +29,16 @@ class ThreadWithCustomScheduler : public WebThread {
 
 }  // namespace
 
-TestingPlatformSupportWithCustomScheduler ::
+TestingPlatformSupportWithCustomScheduler::
     TestingPlatformSupportWithCustomScheduler(ThreadScheduler* scheduler)
-    : thread_(std::make_unique<ThreadWithCustomScheduler>(scheduler)) {}
-
-TestingPlatformSupportWithCustomScheduler ::
-    ~TestingPlatformSupportWithCustomScheduler() {}
-
-WebThread* TestingPlatformSupportWithCustomScheduler::CurrentThread() {
-  DCHECK(WTF::IsMainThread());
-  return thread_.get();
+    : thread_(std::make_unique<ThreadWithCustomScheduler>(scheduler)) {
+  // If main_thread_ is set, Platform::SetCurrentPlatformForTesting() properly
+  // sets up the platform so Platform::CurrentThread() would return the
+  // thread specified here.
+  main_thread_ = thread_.get();
 }
 
+TestingPlatformSupportWithCustomScheduler::
+    ~TestingPlatformSupportWithCustomScheduler() {}
+
 }  // namespace blink

third_party/blink/renderer/platform/testing/testing_platform_support_with_custom_scheduler.h

@@ -26,8 +26,6 @@ class TestingPlatformSupportWithCustomScheduler
       ThreadScheduler* scheduler);
   ~TestingPlatformSupportWithCustomScheduler() override;
 
-  WebThread* CurrentThread() override;
-
  private:
   std::unique_ptr<WebThread> thread_;
 

third_party/blink/renderer/platform/testing/testing_platform_support_with_mock_scheduler.cc

@@ -10,29 +10,10 @@
 #include "third_party/blink/public/platform/scheduler/child/webthread_base.h"
 #include "third_party/blink/renderer/platform/scheduler/main_thread/main_thread_scheduler_impl.h"
 #include "third_party/blink/renderer/platform/waitable_event.h"
-#include "third_party/blink/renderer/platform/wtf/thread_specific.h"
 #include "third_party/blink/renderer/platform/wtf/time.h"
 
 namespace blink {
 
-namespace {
-
-struct ThreadLocalStorage {
-  WebThread* current_thread = nullptr;
-};
-
-ThreadLocalStorage* GetThreadLocalStorage() {
-  DEFINE_THREAD_SAFE_STATIC_LOCAL(ThreadSpecific<ThreadLocalStorage>, tls, ());
-  return tls;
-}
-
-void PrepareCurrentThread(WaitableEvent* event, WebThread* thread) {
-  GetThreadLocalStorage()->current_thread = thread;
-  event->Signal();
-}
-
-}  // namespace
-
 TestingPlatformSupportWithMockScheduler::
     TestingPlatformSupportWithMockScheduler()
     : test_task_runner_(base::MakeRefCounted<base::TestMockTimeTaskRunner>(
@@ -47,6 +28,7 @@ TestingPlatformSupportWithMockScheduler::
   scheduler_ = std::make_unique<scheduler::MainThreadSchedulerImpl>(
       std::move(sequence_manager), base::nullopt);
   thread_ = scheduler_->CreateMainThread();
+  main_thread_ = thread_.get();
   // Set the work batch size to one so TakePendingTasks behaves as expected.
   scheduler_->GetSchedulerHelperForTesting()->SetWorkBatchSizeForTesting(1);
 
@@ -59,31 +41,6 @@ TestingPlatformSupportWithMockScheduler::
   scheduler_->Shutdown();
 }
 
-std::unique_ptr<WebThread>
-TestingPlatformSupportWithMockScheduler::CreateThread(
-    const WebThreadCreationParams& params) {
-  std::unique_ptr<scheduler::WebThreadBase> thread =
-      scheduler::WebThreadBase::CreateWorkerThread(params);
-  thread->Init();
-  WaitableEvent event;
-  thread->GetTaskRunner()->PostTask(
-      FROM_HERE, base::BindOnce(PrepareCurrentThread, base::Unretained(&event),
-                                base::Unretained(thread.get())));
-  event.Wait();
-  return std::move(thread);
-}
-
-WebThread* TestingPlatformSupportWithMockScheduler::CurrentThread() {
-  DCHECK_EQ(thread_->IsCurrentThread(), IsMainThread());
-
-  if (thread_->IsCurrentThread()) {
-    return thread_.get();
-  }
-  ThreadLocalStorage* storage = GetThreadLocalStorage();
-  DCHECK(storage->current_thread);
-  return storage->current_thread;
-}
-
 void TestingPlatformSupportWithMockScheduler::RunSingleTask() {
   base::circular_deque<base::TestPendingTask> tasks =
       test_task_runner_->TakePendingTasks();

third_party/blink/renderer/platform/testing/testing_platform_support_with_mock_scheduler.h

@@ -35,11 +35,6 @@ class TestingPlatformSupportWithMockScheduler : public TestingPlatformSupport {
   TestingPlatformSupportWithMockScheduler();
   ~TestingPlatformSupportWithMockScheduler() override;
 
-  // Platform:
-  std::unique_ptr<WebThread> CreateThread(
-      const WebThreadCreationParams&) override;
-  WebThread* CurrentThread() override;
-
   // Runs a single task.
   void RunSingleTask();