Make cc::SurfaceId unguessable

cc/surfaces/surface_id_allocator.h

 // 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.
 
 #ifndef CC_SURFACES_SURFACE_ID_ALLOCATOR_H_
 #define CC_SURFACES_SURFACE_ID_ALLOCATOR_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 21 matching lines @@
   // When this SurfaceIdAllocator is destroyed, its namespace is
   // automatically invalidated and any remaining sequences with that
   // namespace will be ignored. This method does not need to be called in
   // contexts where there is no SurfaceManager (e.g. a renderer process).
   void RegisterSurfaceIdNamespace(SurfaceManager* manager);
 
   uint32_t id_namespace() const { return id_namespace_; }
 
  private:
   const uint32_t id_namespace_;
-  uint32_t next_id_;
+  uint64_t next_id_;
   SurfaceManager* manager_;
 
   DISALLOW_COPY_AND_ASSIGN(SurfaceIdAllocator);
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_ID_ALLOCATOR_H_