Partial revert of 'Refactor CompositorWorkerManager'

This is a partial revert of:
https://codereview.chromium.org/1449953002

Most of that CL is inactive code, but it did change the way the
compositor thread was created. Instead of a base::Thread, I'd used a
WebThreadImplForWorkerScheduler and this seems to have had some
performance impact. While I try to figure out why, this CL should get
us back to our prior performance.

BUG=565789

Review URL: https://codereview.chromium.org/1550093002

Cr-Commit-Position: refs/heads/master@{#367051}

content/renderer/render_thread_impl.cc

@@ -1150,18 +1150,18 @@ void RenderThreadImpl::InitializeCompositorThread() {
   }
 #endif
   if (!compositor_task_runner_.get()) {
-    base::Thread::Options options;
+
+    compositor_thread_.reset(new base::Thread("Compositor"));
+    base::Thread::Options compositor_thread_options;
 #if defined(OS_ANDROID)
-    options.priority = base::ThreadPriority::DISPLAY;
+    compositor_thread_options.priority = base::ThreadPriority::DISPLAY;
 #endif
-    compositor_thread_ =
-        blink_platform_impl_->createThreadWithOptions("Compositor", options);
-    compositor_task_runner_ = compositor_thread_->TaskRunner();
+    compositor_thread_->StartWithOptions(compositor_thread_options);
+    compositor_task_runner_ = compositor_thread_->task_runner();
     compositor_task_runner_->PostTask(
         FROM_HERE,
         base::Bind(base::IgnoreResult(&ThreadRestrictions::SetIOAllowed),
                    false));
-    blink_platform_impl_->set_compositor_thread(compositor_thread_.get());
   }
 
   InputHandlerManagerClient* input_handler_manager_client = NULL;

content/renderer/render_thread_impl.h

@@ -600,7 +600,7 @@ class CONTENT_EXPORT RenderThreadImpl
   scoped_ptr<base::Thread> file_thread_;
 
   // May be null if overridden by ContentRendererClient.
-  scoped_ptr<scheduler::WebThreadBase> compositor_thread_;
+  scoped_ptr<base::Thread> compositor_thread_;
 
   // Utility class to provide GPU functionalities to media.
   scoped_ptr<content::RendererGpuVideoAcceleratorFactories> gpu_factories_;