content: Add an overridable task runner to ChildThreadImpl

content/renderer/render_thread_impl.h

Index: content/renderer/render_thread_impl.h
diff --git a/content/renderer/render_thread_impl.h b/content/renderer/render_thread_impl.h
index 26de62bfa6b56b41a04dbbc91116e43eb5d75f63..a04c25b5ace188184a7b056dd3389892acfc5389 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -131,11 +131,13 @@ class CONTENT_EXPORT RenderThreadImpl
  public:
   static RenderThreadImpl* current();
 
-  RenderThreadImpl();
+  explicit RenderThreadImpl(scoped_ptr<RendererScheduler> renderer_scheduler);
   // Constructor that's used when running in single process mode.
-  explicit RenderThreadImpl(const std::string& channel_name);
+  RenderThreadImpl(const std::string& channel_name,
+                   scoped_ptr<RendererScheduler> renderer_scheduler);
   // Constructor that's used in RendererMain.
-  explicit RenderThreadImpl(scoped_ptr<base::MessageLoop> main_message_loop);
+  RenderThreadImpl(scoped_ptr<base::MessageLoop> main_message_loop,
+                   scoped_ptr<RendererScheduler> renderer_scheduler);
   ~RenderThreadImpl() override;
   void Shutdown() override;