Implement temporary reference assignment with DisplayCompositor.

cc/ipc/display_compositor.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module cc.mojom;
 
 import "cc/ipc/frame_sink_id.mojom";
 import "cc/ipc/local_surface_id.mojom";
 import "cc/ipc/mojo_compositor_frame_sink.mojom";
 import "cc/ipc/surface_id.mojom";
@@ skipping 39 matching lines @@
       associated DisplayPrivate& display_private);
 
   // CreateCompositorFrameSink is used by unprivileged clients.
   // This CompositorFrameSink is not a root, and has to be parented by another
   // CompositorFrameSink in order to appear on screen.
   CreateCompositorFrameSink(
       cc.mojom.FrameSinkId frame_sink_id,
       cc.mojom.MojoCompositorFrameSink& compositor_frame_sink,
       cc.mojom.MojoCompositorFrameSinkPrivate& compositor_frame_sink_private,
       cc.mojom.MojoCompositorFrameSinkClient compositor_frame_sink_client);
+
+  // Drops the temporary reference for |surface_id|. This will get called when
+  // the DisplayCompositorClient doesn't think |surface_id| will be embedded.
+  DropTemporaryReference(cc.mojom.SurfaceId surface_id);
 };
 
 // The DisplayCompositorClient interface is implemented by the Display
 // Compositor Host, a stable, and privileged peer service to the display
 // compositor. The display compositor host is either the browser process in
 // Chrome or the window server process.
 interface DisplayCompositorClient {
   // Called by the display compositor immediately upon receiving a
   // CompositorFrame with a new SurfaceId for the first time.
   OnSurfaceCreated(SurfaceInfo surface_info);
 };