Refactor the PlatformContext layer to have only one class.

skia/ext/platform_device.h

 // Copyright (c) 2006-2008 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.
 
-// Declare a platform-neutral name for this platform's device class
-// that can be used by upper-level classes that just need to pass a reference
-// around.
+#ifndef SKIA_EXT_PLATFORM_DEVICE_H_
+#define SKIA_EXT_PLATFORM_DEVICE_H_
+
+// This file provides an easy way to include the appropriate PlatformDevice
+// header file for your platform.
 
 #if defined(WIN32)
 #include "skia/ext/platform_device_win.h"
 #elif defined(__APPLE__)
 #include "skia/ext/platform_device_mac.h"
 #elif defined(__linux__)
 #include "skia/ext/platform_device_linux.h"
 #endif
 
-namespace skia {
-
-#if defined(WIN32)
-typedef PlatformDeviceWin PlatformDevice;
-#elif defined(__APPLE__)
-typedef PlatformDeviceMac PlatformDevice;
-#elif defined(__linux__)
-typedef PlatformDeviceLinux PlatformDevice;
 #endif
-
-}  // namespace skia