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

content/browser/compositor/surface_display_output_surface.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 "content/browser/compositor/surface_display_output_surface.h"
 
 #include "cc/output/compositor_frame.h"
 #include "cc/surfaces/display.h"
 #include "cc/surfaces/surface.h"
 #include "cc/surfaces/surface_manager.h"
@@ skipping 12 matching lines @@
   capabilities_.max_frames_pending = 1;
 }
 
 SurfaceDisplayOutputSurface::~SurfaceDisplayOutputSurface() {
 }
 
 void SurfaceDisplayOutputSurface::SwapBuffers(cc::CompositorFrame* frame) {
   gfx::Size frame_size =
       frame->delegated_frame_data->render_pass_list.back()->output_rect.size();
   display_->Resize(frame_size);
-  int surface_id = display_->CurrentSurfaceID();
-  cc::Surface* surface = surface_manager_->GetSurfaceForID(surface_id);
+  cc::SurfaceId surface_id = display_->CurrentSurfaceId();
+  cc::Surface* surface = surface_manager_->GetSurfaceForId(surface_id);
   if (!surface)
     return;
 
   scoped_ptr<cc::CompositorFrame> frame_copy(new cc::CompositorFrame());
   frame->AssignTo(frame_copy.get());
   surface->QueueFrame(frame_copy.Pass());
 
   if (!display_->Draw())
     return;
 
   client_->DidSwapBuffers();
   client_->DidSwapBuffersComplete();
 }
 
 }  // namespace content