rename getBitmapDC to beginPlatformPaint and add calls to endPlatformPaint

skia/ext/platform_canvas.h

 // 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.
 
 #ifndef SKIA_EXT_PLATFORM_CANVAS_H_
 #define SKIA_EXT_PLATFORM_CANVAS_H_
 #pragma once
 
 // The platform-specific device will include the necessary platform headers
 // to get the surface type.
@@ skipping 51 matching lines @@
 #endif
 
   // Shared --------------------------------------------------------------------
 
   // These calls should surround calls to platform drawing routines, the
   // surface returned here can be used with the native platform routines
   //
   // Call endPlatformPaint when you are done and want to use Skia operations
   // after calling the platform-specific beginPlatformPaint; this will
   // synchronize the bitmap to OS if necessary.
-  PlatformDevice::PlatformSurface beginPlatformPaint();
-  void endPlatformPaint();
+  PlatformDevice::PlatformSurface beginPlatformPaint() const;
+  void endPlatformPaint() const;
 
   // Returns the platform device pointer of the topmost rect with a non-empty
   // clip. In practice, this is usually either the top layer or nothing, since
   // we usually set the clip to new layers when we make them.
   //
   // If there is no layer that is not all clipped out, this will return a
   // dummy device so callers do not have to check. If you are concerned about
   // performance, check the clip before doing any painting.
   //
   // This is different than SkCanvas' getDevice, because that returns the
@@ skipping 26 matching lines @@
   virtual SkDevice* setBitmapDevice(const SkBitmap& bitmap);
 
   // Disallow copy and assign.
   PlatformCanvas(const PlatformCanvas&);
   PlatformCanvas& operator=(const PlatformCanvas&);
 };
 
 }  // namespace skia
 
 #endif  // SKIA_EXT_PLATFORM_CANVAS_H_