Create manager to track OffscreenCanvasSurfaceImpl instances

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 f4e4448d561060e6fd9d53c0f2bae50a8f2d5c4e..d45c7d25ec812f79f2b3436b61a31a494df417ce 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
@@ -14,14 +14,15 @@ interface OffscreenCanvasSurface {
   // change on surface_id generator that makes client side be able to generate
   // unique surface_id.id_namespace alone.
   [Sync]
-  GetSurfaceId() => (cc.mojom.SurfaceId surface_id);
+  GetSurfaceId(uint32 canvas_id) => (cc.mojom.SurfaceId surface_id);

[dcheng, 2016/11/08 18:30:23]

Help me understand =)

What is canvas id? why do we need to identify these with canvas ids?

[xlai (Olivia), 2016/11/10 15:45:11]

Canvas ID is a unique identifier for an HTMLCanvasElement. Actually, it is just
a unique ID for every DOM object.

We need to identify different canvas ID because we want to handle the case when
there are multiple HTMLCanvasElement transfer control
to Offscreen. In this case, the browser side needs to distinguish which
HTMLCanvasElement is making a request to the browser.

[dcheng, 2016/11/11 08:36:40]

In a Mojo world though, I would expect the endpoints to be associated by virtue
of having a connected interface. We shouldn't need numeric IDs to associate
different endpoints.

 
   Require(cc.mojom.SurfaceId surface_id, cc.mojom.SurfaceSequence sequence);
   Satisfy(cc.mojom.SurfaceSequence sequence);
 };
 
 interface OffscreenCanvasCompositorFrameSinkProvider {
-  CreateCompositorFrameSink(cc.mojom.SurfaceId surface_id,
+  CreateCompositorFrameSink(uint32 canvas_id,
+                            cc.mojom.SurfaceId surface_id,
                             cc.mojom.MojoCompositorFrameSinkClient client,
                             cc.mojom.MojoCompositorFrameSink& sink);
 };