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 49 matching lines @@
 
   // Set up a BeginFrame relationship between two FrameSinkIds. In this case,
   // the child inherits the BeginFrameSource from the parent if it doesn't
   // already have a BeginFrameSource.
   RegisterFrameSinkHierarchy(cc.mojom.FrameSinkId parent_frame_sink_id,
                              cc.mojom.FrameSinkId child_frame_sink_id);
 
   // Removes a BeginFrame relationship between two FrameSinkIds.
   UnregisterFrameSinkHierarchy(cc.mojom.FrameSinkId parent_frame_sink_id,
                                cc.mojom.FrameSinkId child_frame_sink_id);
+
+  // 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);
 };