Reland of placing allocate bitmap IPC messages with a new Mojo interface.

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 0124bb925ecaebd9a88af7c650eb588c63927842..e3c7b9c23610df2a24252c67c13b3041a0672bd5 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -110,6 +110,7 @@
 class BrowserPluginManager;
 class CacheStorageDispatcher;
 class ChildGpuMemoryBufferManager;
+class ChildSharedBitmapManager;
 class CompositorForwardingMessageFilter;
 class ContextProviderCommandBuffer;
 class DBMessageFilter;
@@ -352,6 +353,11 @@
     return vc_manager_.get();
   }
 
+  ChildSharedBitmapManager* shared_bitmap_manager() const {
+    DCHECK(shared_bitmap_manager_);
+    return shared_bitmap_manager_.get();
+  }
+
   mojom::RenderFrameMessageFilter* render_frame_message_filter();
   mojom::RenderMessageFilter* render_message_filter();
   const scoped_refptr<mojom::ThreadSafeRenderMessageFilterAssociatedPtr>&
@@ -609,6 +615,8 @@
   std::unique_ptr<ThreadSafeAssociatedInterfacePtrProvider>
       thread_safe_associated_interface_ptr_provider_;
 
+  std::unique_ptr<ChildSharedBitmapManager> shared_bitmap_manager_;
+
   // The count of RenderWidgets running through this thread.
   int widget_count_;