rename getBitmapDC to beginPlatformPaint and add calls to endPlatformPaint

skia/ext/platform_canvas_mac.cc

-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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 "skia/ext/platform_canvas.h"
 
 #include "skia/ext/bitmap_platform_device_mac.h"
 #include "third_party/skia/include/core/SkTypes.h"
 
 namespace skia {
 
@@ skipping 30 matching lines @@
 }
 
 bool PlatformCanvas::initialize(CGContextRef context,
                                 int width,
                                 int height,
                                 bool is_opaque) {
   return initializeWithDevice(BitmapPlatformDevice::Create(
       context, width, height, is_opaque));
 }
 
-CGContextRef PlatformCanvas::beginPlatformPaint() {
+CGContextRef PlatformCanvas::beginPlatformPaint() const {
   return getTopPlatformDevice().GetBitmapContext();
 }
 
-void PlatformCanvas::endPlatformPaint() {
+void PlatformCanvas::endPlatformPaint() const {
   // Flushing will be done in onAccessBitmap.
 }
 
 }  // namespace skia