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

ui/surface/transport_dib_linux.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 <errno.h>
 #include <stdlib.h>
 #include <sys/ipc.h>
 #include <sys/shm.h>
@@ skipping 76 matching lines @@
 }
 
 // static
 bool TransportDIB::is_valid_id(Id id) {
   return id.shmkey != -1;
 }
 
 skia::PlatformCanvas* TransportDIB::GetPlatformCanvas(int w, int h) {
   if (address_ == kInvalidAddress && !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_id(key_))
     return false;
   if (address_ != kInvalidAddress)
     return true;
 
   struct shmid_ds shmst;
   if (shmctl(key_.shmkey, IPC_STAT, &shmst) == -1)
@@ skipping 36 matching lines @@
   if (!inflight_counter_ && detached_)
     delete this;
 }
 
 void TransportDIB::Detach() {
   CHECK(!detached_);
   detached_ = true;
   if (!inflight_counter_)
     delete this;
 }