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

content/public/test/mock_render_thread.cc

Index: content/public/test/mock_render_thread.cc
diff --git a/content/public/test/mock_render_thread.cc b/content/public/test/mock_render_thread.cc
index a292f78d752c1b3694b34e80591599086e71c516..1003a2bc92fcf7baef4569701a63a4de9649b585 100644
--- a/content/public/test/mock_render_thread.cc
+++ b/content/public/test/mock_render_thread.cc
@@ -72,6 +72,15 @@
   void CreateFullscreenWidget(
       int opener_id,
       const CreateFullscreenWidgetCallback& callback) override {
+    NOTREACHED();
+  }
+
+  void AllocatedSharedBitmap(mojo::ScopedSharedBufferHandle buffer,
+                             const cc::SharedBitmapId& id) override {
+    NOTREACHED();
+  }
+
+  void DeletedSharedBitmap(const cc::SharedBitmapId& id) override {
     NOTREACHED();
   }