Move the "platform" wrappers in skia/ext to the skia namespace.

skia/ext/platform_canvas.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 canvas class
 // that can be used by upper-level classes that just need to pass a reference
 // around.
 
 #if defined(WIN32)
 #include "skia/ext/platform_canvas_win.h"
-namespace gfx {
-
-typedef PlatformCanvasWin PlatformCanvas;
-
-}  // namespace gfx
 #elif defined(__APPLE__)
 #include "skia/ext/platform_canvas_mac.h"
-namespace gfx {
-
-typedef PlatformCanvasMac PlatformCanvas;
-
-}  // namespace gfx
 #elif defined(__linux__)
 #include "skia/ext/platform_canvas_linux.h"
-namespace gfx {
+#endif
 
+namespace skia {
+
+#if defined(WIN32)
+typedef PlatformCanvasWin PlatformCanvas;
+#elif defined(__APPLE__)
+typedef PlatformCanvasMac PlatformCanvas;
+#elif defined(__linux__)
 typedef PlatformCanvasLinux PlatformCanvas;
+#endif
 
-}  // namespace gfx
-#endif
+}  // namespace skia