content/blimp: Set up hooks for enabling LTHRemote in the renderer.

cc/proto/compositor_message.proto

Index: cc/proto/compositor_message.proto
diff --git a/cc/proto/compositor_message.proto b/cc/proto/compositor_message.proto
index 0697a18611d88352997ad786d28c1445081bd202..41f3f51cb9183530c64fefa0cbfbf129e9b5dde6 100644
--- a/cc/proto/compositor_message.proto
+++ b/cc/proto/compositor_message.proto
@@ -21,6 +21,10 @@ message CompositorMessage {
   // Frame Update.
   optional LayerTreeHost layer_tree_host = 3;
 
+  // Client -> Engine
+  // Frame Ack.

[danakj, 2016/10/13 19:23:23]

The comment is literally the same text as the variable name, can you say what it
is instead of its name?

[Khushal, 2016/10/13 20:03:57]

Done.

+  optional bool frame_ack = 4;
+
   // One of these is set based on where the message is going to.
   optional CompositorMessageToMain to_main = 1;
   optional CompositorMessageToImpl to_impl = 2;