Change transport dib API to not make copies of SharedMemoryHandle.

ui/surface/transport_dib.cc

 // Copyright (c) 2013 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 "ui/surface/transport_dib.h"
 
 #include "skia/ext/platform_canvas.h"
 
 // static
 bool TransportDIB::VerifyCanvasSize(int w, int h) {
   static const size_t kMaxSize = static_cast<size_t>(INT_MAX);
   const size_t one_stride = skia::PlatformCanvasStrideForWidth(1);
   const size_t stride = skia::PlatformCanvasStrideForWidth(w);
   if (w <= 0 || h <= 0 || static_cast<size_t>(w) > (kMaxSize / one_stride) ||
       static_cast<size_t>(h) > (kMaxSize / stride)) {
     return false;
   }
 
   return (stride * h) <= size_;
 }
 
+base::SharedMemory* TransportDIB::shared_memory() {
+  return &shared_memory_;
+}