Change call-sites now that SkCanvas is not ref-counted

ui/surface/transport_dib_posix.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 <stddef.h>
 #include <stdint.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ skipping 40 matching lines @@
 // static
 TransportDIB* TransportDIB::CreateWithHandle(Handle handle) {
   return new TransportDIB(handle);
 }
 
 // static
 bool TransportDIB::is_valid_handle(Handle dib) {
   return base::SharedMemory::IsHandleValid(dib);
 }
 
-SkCanvas* TransportDIB::GetPlatformCanvas(int w, int h, bool opaque) {
+std::unique_ptr<SkCanvas> TransportDIB::GetPlatformCanvas(int w,
+                                                          int h,
+                                                          bool opaque) {
   if ((!memory() && !Map()) || !VerifyCanvasSize(w, h))
     return NULL;
   return skia::CreatePlatformCanvas(w, h, opaque,
                                     reinterpret_cast<uint8_t*>(memory()),
                                     skia::RETURN_NULL_ON_FAILURE);
 }
 
 bool TransportDIB::Map() {
   if (!is_valid_handle(shared_memory_.handle()))
     return false;
@@ skipping 12 matching lines @@
     return false;
 
   size_ = size;
 #endif
   return true;
 }
 
 void* TransportDIB::memory() const {
   return shared_memory_.memory();
 }