Use a struct for cc::Surface ids for more type safety

cc/surfaces/display.cc

 // Copyright 2014 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.
 
 #include "cc/surfaces/display.h"
 
 #include "base/message_loop/message_loop.h"
 #include "cc/output/compositor_frame.h"
 #include "cc/output/direct_renderer.h"
 #include "cc/output/gl_renderer.h"
@@ skipping 136 matching lines @@
   renderer_->DrawFrame(&frame_data->render_pass_list,
                        device_scale_factor,
                        device_viewport_rect,
                        device_clip_rect,
                        disable_picture_quad_image_filtering);
   CompositorFrameMetadata metadata;
   renderer_->SwapBuffers(metadata);
   return true;
 }
 
-int Display::CurrentSurfaceID() {
-  return current_surface_ ? current_surface_->surface_id() : 0;
+SurfaceId Display::CurrentSurfaceId() {
+  return current_surface_ ? current_surface_->surface_id() : SurfaceId();
 }
 
 void Display::ReturnResources(const ReturnedResourceArray& resources) {
 }
 
 }  // namespace cc