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

cc/surfaces/surface_manager.h

Index: cc/surfaces/surface_manager.h
diff --git a/cc/surfaces/surface_manager.h b/cc/surfaces/surface_manager.h
index fe12dbfc5d01edfd1afeb15865128e0ebbfbe284..b14259d63def7aa26222b00c09bbd5565d3bce0b 100644
--- a/cc/surfaces/surface_manager.h
+++ b/cc/surfaces/surface_manager.h
@@ -7,23 +7,23 @@
 
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
+#include "cc/surfaces/surface_id.h"
 #include "cc/surfaces/surfaces_export.h"
 
-namespace gfx { class Size; }
-
 namespace cc {
 class CompositorFrame;
 class Surface;
+class SurfaceClient;
 
 class CC_SURFACES_EXPORT SurfaceManager {
  public:
   SurfaceManager();
   ~SurfaceManager();
 
-  int RegisterAndAllocateIDForSurface(Surface* surface);
-  void DeregisterSurface(int surface_id);
+  SurfaceId RegisterAndAllocateIdForSurface(Surface* surface);
+  void DeregisterSurface(SurfaceId surface_id);
 
-  Surface* GetSurfaceForID(int surface_id);
+  Surface* GetSurfaceForId(SurfaceId surface_id);
 
  private:
   typedef base::hash_map<int, Surface*> SurfaceMap;