WIP: move OffscreenCanvas into new display compositor

cc/ipc/display_compositor.mojom

Index: cc/ipc/display_compositor.mojom
diff --git a/cc/ipc/display_compositor.mojom b/cc/ipc/display_compositor.mojom
index bd0e942844edfe09cbbf536c53f06dcdc64c16a4..55e0f16b613e2319a309dd0f1d1114f1c140709b 100644
--- a/cc/ipc/display_compositor.mojom
+++ b/cc/ipc/display_compositor.mojom
@@ -57,6 +57,13 @@ interface DisplayCompositor {
       cc.mojom.MojoCompositorFrameSink& compositor_frame_sink,
       cc.mojom.MojoCompositorFrameSinkPrivate& compositor_frame_sink_private,
       cc.mojom.MojoCompositorFrameSinkClient compositor_frame_sink_client);
+
+  // CreateOffscreenCanvasCompositorFrameSink is used by OffscreenCanvas.
+  CreateOffscreenCanvasCompositorFrameSink(

[Fady Samuel, 2017/02/21 14:16:18]

I don't think we should special case offscreen canvas. It should be no different
from any other client.

+      cc.mojom.FrameSinkId frame_sink_id,
+      cc.mojom.MojoCompositorFrameSink& compositor_frame_sink,
+      cc.mojom.MojoCompositorFrameSinkClient compositor_frame_sink_client);
+
 };
 
 // The DisplayCompositorClient interface is implemented by the Display