Reland of cc: Add mailbox support to ResourceProvider write locks.

cc/tiles/tile_task_manager.h

Index: cc/tiles/tile_task_manager.h
diff --git a/cc/tiles/tile_task_manager.h b/cc/tiles/tile_task_manager.h
index 60294d6722d72a28562c082e7cbe2c6aa743d9a8..7f543c10d15ebf34ec1ddbd2efa6c6cbb287064b 100644
--- a/cc/tiles/tile_task_manager.h
+++ b/cc/tiles/tile_task_manager.h
@@ -32,9 +32,6 @@ class CC_EXPORT TileTaskManager {
 
   // Shutdown after canceling all previously scheduled tasks.
   virtual void Shutdown() = 0;
-
-  // Get RasterBufferProvider.
-  virtual RasterBufferProvider* GetRasterBufferProvider() const = 0;
 };
 
 class CC_EXPORT TileTaskManagerImpl : public TileTaskManager {
@@ -42,21 +39,16 @@ class CC_EXPORT TileTaskManagerImpl : public TileTaskManager {
   ~TileTaskManagerImpl() override;
 
   static std::unique_ptr<TileTaskManagerImpl> Create(
-      std::unique_ptr<RasterBufferProvider> raster_buffer_provider,
       TaskGraphRunner* task_graph_runner);
 
   // Overridden from TileTaskManager:
   void ScheduleTasks(TaskGraph* graph) override;
   void CheckForCompletedTasks() override;
   void Shutdown() override;
-  RasterBufferProvider* GetRasterBufferProvider() const override;
 
  protected:
-  TileTaskManagerImpl(
-      std::unique_ptr<RasterBufferProvider> raster_buffer_provider,
-      TaskGraphRunner* task_graph_runner);
+  explicit TileTaskManagerImpl(TaskGraphRunner* task_graph_runner);
 
-  std::unique_ptr<RasterBufferProvider> raster_buffer_provider_;
   TaskGraphRunner* task_graph_runner_;
   const NamespaceToken namespace_token_;