Simplify platform_canvas.h by recognizing that PlatformCanvas does not actually extend

ui/surface/transport_dib_mac.cc

 // Copyright (c) 2012 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 <sys/stat.h>
 #include <unistd.h>
 
 #include "base/eintr_wrapper.h"
@@ skipping 45 matching lines @@
 }
 
 // static
 bool TransportDIB::is_valid_id(Id id) {
   return id != 0;
 }
 
 skia::PlatformCanvas* TransportDIB::GetPlatformCanvas(int w, int h) {
   if (!memory() && !Map())
     return NULL;
-  scoped_ptr<skia::PlatformCanvas> canvas(new skia::PlatformCanvas);
-  if (!canvas->initialize(w, h, true, reinterpret_cast<uint8_t*>(memory())))
-    return NULL;
-  return canvas.release();
+  return skia::CreatePlatformCanvas(w, h, true, 
+                                    reinterpret_cast<uint8_t*>(memory()),
+                                    skia::RETURN_NULL_ON_FAILURE);
 }
 
 bool TransportDIB::Map() {
   if (!is_valid_handle(handle()))
     return false;
   if (memory())
     return true;
 
   struct stat st;
   if ((fstat(shared_memory_.handle().fd, &st) != 0) ||
       (!shared_memory_.Map(st.st_size))) {
     return false;
   }
 
   size_ = st.st_size;
   return true;
 }
 
 void* TransportDIB::memory() const {
   return shared_memory_.memory();
 }
 
 TransportDIB::Id TransportDIB::id() const {
   return shared_memory_.id();
 }
 
 TransportDIB::Handle TransportDIB::handle() const {
   return shared_memory_.handle();
 }