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"
 #include "cc/surfaces/surface_id.h"
 #include "cc/surfaces/surfaces_export.h"
 
 namespace cc {
 
 class SurfaceManager;
 
 // This is a helper class for generating surface IDs within a specified
 // namespace.  This is not threadsafe, to use from multiple threads wrap this
 // class in a mutex.
 class CC_SURFACES_EXPORT SurfaceIdAllocator {
  public:
   explicit SurfaceIdAllocator(uint32_t id_namespace);
   ~SurfaceIdAllocator();
 
   SurfaceId GenerateId();
 
-  static uint32_t NamespaceForId(SurfaceId id);
-
   // This needs to be called before any sequences with this allocator's
   // namespace will be used to enforce destruction dependencies.
   // 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_;
   SurfaceManager* manager_;
 
   DISALLOW_COPY_AND_ASSIGN(SurfaceIdAllocator);
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_ID_ALLOCATOR_H_