ui/gfx: Make gfx::Canvas inherit from gfx::CanvasSkia.

ui/gfx/canvas_skia_mac.mm

 // 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.
 
 #import <Cocoa/Cocoa.h>
 
-#include "ui/gfx/canvas_skia.h"
+#include "ui/gfx/canvas.h"
 
 #include "base/logging.h"
 #include "base/sys_string_conversions.h"
 #include "third_party/skia/include/core/SkTypeface.h"
 #include "ui/gfx/font.h"
 
 // Note: This is a temporary Skia-based implementation of the ui/gfx text
 // rendering routines for views/aura.  It replaces the stale Cocoa-based
 // implementation.  A future |canvas_skia_skia.cc| implementation will supersede
 // this and the other platform-specific implmenentations.
@@ skipping 52 matching lines @@
 
 void CanvasSkia::DrawStringWithHalo(const string16& text,
                                     const gfx::Font& font,
                                     const SkColor& text_color,
                                     const SkColor& halo_color,
                                     int x, int y, int w, int h,
                                     int flags) {
 }
 
 }  // namespace gfx