Replaced cc::SurfaceId::nonce_ with base::UnguessableToken

cc/surfaces/surface_id_allocator.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 "cc/surfaces/surface_id_allocator.h"
 
 #include <stdint.h>
 
-#include "base/rand_util.h"
-
 namespace cc {
 
 SurfaceIdAllocator::SurfaceIdAllocator(uint32_t client_id)
     : client_id_(client_id), next_id_(1u) {}
 
 SurfaceIdAllocator::~SurfaceIdAllocator() {
 }
 
 SurfaceId SurfaceIdAllocator::GenerateId() {
-  uint64_t nonce = base::RandUint64();
-  SurfaceId id(client_id_, next_id_, nonce);
+  SurfaceId id(client_id_, next_id_);
   next_id_++;
   return id;
 }
 
 }  // namespace cc