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

cc/surfaces/surface_aggregator.h

Index: cc/surfaces/surface_aggregator.h
diff --git a/cc/surfaces/surface_aggregator.h b/cc/surfaces/surface_aggregator.h
index 4115bc39a1f9c296a6e4869a2ab642b4adb216f9..fe52050503f9bb5dc81e0881b471fbf93ec55fa9 100644
--- a/cc/surfaces/surface_aggregator.h
+++ b/cc/surfaces/surface_aggregator.h
@@ -10,6 +10,7 @@
 #include "base/containers/scoped_ptr_hash_map.h"
 #include "base/memory/scoped_ptr.h"
 #include "cc/quads/render_pass.h"
+#include "cc/surfaces/surface_id.h"
 #include "cc/surfaces/surfaces_export.h"
 
 namespace cc {
@@ -24,10 +25,10 @@ class CC_SURFACES_EXPORT SurfaceAggregator {
   explicit SurfaceAggregator(SurfaceManager* manager);
   ~SurfaceAggregator();
 
-  scoped_ptr<CompositorFrame> Aggregate(int surface_id);
+  scoped_ptr<CompositorFrame> Aggregate(SurfaceId surface_id);
 
  private:
-  DelegatedFrameData* GetReferencedDataForSurfaceID(int surface_id);
+  DelegatedFrameData* GetReferencedDataForSurfaceId(SurfaceId surface_id);
   RenderPass::Id RemapPassId(RenderPass::Id surface_local_pass_id,
                              int surface_id);