Reintroduce OffscreenCanvasSurfaceClient interface.

third_party/WebKit/public/platform/modules/offscreencanvas/offscreen_canvas_surface.mojom

Index: third_party/WebKit/public/platform/modules/offscreencanvas/offscreen_canvas_surface.mojom
diff --git a/third_party/WebKit/public/platform/modules/offscreencanvas/offscreen_canvas_surface.mojom b/third_party/WebKit/public/platform/modules/offscreencanvas/offscreen_canvas_surface.mojom
index d17270b081c7af69886d1ecc99976ec62792cc25..7d57beea8fc899c776079cde468266a864937956 100644
--- a/third_party/WebKit/public/platform/modules/offscreencanvas/offscreen_canvas_surface.mojom
+++ b/third_party/WebKit/public/platform/modules/offscreencanvas/offscreen_canvas_surface.mojom
@@ -8,6 +8,7 @@ import "cc/ipc/frame_sink_id.mojom";
 import "cc/ipc/frame_sink_manager.mojom";
 import "cc/ipc/mojo_compositor_frame_sink.mojom";
 import "cc/ipc/surface_id.mojom";
+import "cc/ipc/surface_info.mojom";
 import "cc/ipc/surface_sequence.mojom";
 
 interface OffscreenCanvasSurface {
@@ -15,15 +16,18 @@ interface OffscreenCanvasSurface {
   Satisfy(cc.mojom.SurfaceSequence sequence);
 };
 
+interface OffscreenCanvasSurfaceClient {
+  OnSurfaceCreated(cc.mojom.SurfaceInfo surface_info);
+};
+
 // Creates OffscreenCanvasSurface and MojoCompositorFrameSink instances for use
 // with offscreen canvas.
 interface OffscreenCanvasProvider {
-  // TODO(kylechar): Observer interface shouldn't be FrameSinkManagerClient.
   // Create an OffscreenCanvasSurface for |frame_sink_id|. |client| will observe
   // any changes to the SurfaceId associated with |frame_sink_id|.
   CreateOffscreenCanvasSurface(cc.mojom.FrameSinkId parent_frame_sink_id,
                                cc.mojom.FrameSinkId frame_sink_id,
-                               cc.mojom.FrameSinkManagerClient client,
+                               OffscreenCanvasSurfaceClient client,
                                OffscreenCanvasSurface& surface);
 
   // Create an MojoCompositorFrameSink for |frame_sink_id|. This must happen