[unseasoned-pdf] Initialize gin::IsolateHolder for utility processes

When the "PdfUnseasoned" feature is enabled, gin::IsolateHolder
usually doesn't require being initialized because the plugin code lives
in a renderer process, where Blink has already performed the
initialization.

However, some utility processes use also use PDFium, and they still
require initialization.

Provide gin::IsolateHolder::Initialized() so PDFium can determine
whether the initialization has already been invoked.

Fixed: 1229814
Change-Id: I0e381297af32c9c615f06c92e882640b0012a522
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3033198
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#902309}

gin/isolate_holder.cc

@@ -55,11 +55,14 @@ IsolateHolder::IsolateHolder(
     IsolateType isolate_type,
     IsolateCreationMode isolate_creation_mode)
     : access_mode_(access_mode), isolate_type_(isolate_type) {
+  CHECK(Initialized())
+      << "You need to invoke gin::IsolateHolder::Initialize first";
+
   DCHECK(task_runner);
   DCHECK(task_runner->BelongsToCurrentThread());
 
   v8::ArrayBuffer::Allocator* allocator = g_array_buffer_allocator;
-  CHECK(allocator) << "You need to invoke gin::IsolateHolder::Initialize first";
+  DCHECK(allocator);
 
   isolate_ = v8::Isolate::Allocate();
   isolate_data_ = std::make_unique<PerIsolateData>(isolate_, allocator,
@@ -112,6 +115,11 @@ void IsolateHolder::Initialize(ScriptMode mode,
   g_reference_table = reference_table;
 }
 
+// static
+bool IsolateHolder::Initialized() {
+  return g_array_buffer_allocator;
+}
+
 void IsolateHolder::EnableIdleTasks(
     std::unique_ptr<V8IdleTaskRunner> idle_task_runner) {
   DCHECK(isolate_data_.get());

gin/public/isolate_holder.h

@@ -91,6 +91,11 @@ class GIN_EXPORT IsolateHolder {
                          v8::ArrayBuffer::Allocator* allocator,
                          const intptr_t* reference_table = nullptr);
 
+  // Returns whether `Initialize` has already been invoked in the process.
+  // Initialization is a one-way operation (i.e., this method cannot return
+  // false after returning true).
+  static bool Initialized();
+
   v8::Isolate* isolate() { return isolate_; }
 
   // This method returns if v8::Locker is needed to access isolate.

pdf/pdfium/pdfium_engine.cc

@@ -247,7 +247,7 @@ bool IsV8Initialized() {
 }
 
 void SetUpV8() {
-  if (!base::FeatureList::IsEnabled(features::kPdfUnseasoned)) {
+  if (!gin::IsolateHolder::Initialized()) {
     // TODO(crbug.com/1111024): V8 flags for the Unseasoned Viewer need to be
     // set up as soon as the renderer process is created in the constructor of
     // `content::RenderProcessImpl`.