compositor worker: Use a WebThread for the compositor thread.

content/child/blink_platform_impl.h

Index: content/child/blink_platform_impl.h
diff --git a/content/child/blink_platform_impl.h b/content/child/blink_platform_impl.h
index 1a2b5ab778860d80614cda7798a44fc3fffccaeb..fd066906b5d11f94c213747bd596bb0c4a7bb866 100644
--- a/content/child/blink_platform_impl.h
+++ b/content/child/blink_platform_impl.h
@@ -191,15 +191,15 @@ class CONTENT_EXPORT BlinkPlatformImpl
       const char* name,
       base::Thread::Options);
 
-  // This class does *not* own |compositor_thread|. It is the responsibility of
-  // the caller to ensure that the compositor thread is cleared before it is
+  // This class does *not* own the compositor thread. It is the responsibility
+  // of the caller to ensure that the compositor thread is cleared before it is
   // destructed.
-  void set_compositor_thread(scheduler::WebThreadBase* compositor_thread) {
-    compositor_thread_ = compositor_thread;
-  }
+  scoped_ptr<scheduler::WebThreadBase> createCompositorThread();
+  void reset_compositor_thread() { compositor_thread_ = nullptr; }
 
  private:
   void InternalInit();
+  void WaitUntilWebThreadTLSUpdate(scheduler::WebThreadBase* thread);
   void UpdateWebThreadTLS(blink::WebThread* thread, base::WaitableEvent* event);
 
   bool IsMainThread() const;