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

ui/gfx/render_text_win.h

 // 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.
 
 #ifndef UI_GFX_RENDER_TEXT_WIN_H_
 #define UI_GFX_RENDER_TEXT_WIN_H_
 #pragma once
 
 #include <usp10.h>
 
@@ skipping 69 matching lines @@
   virtual SelectionModel AdjacentWordSelectionModel(
       const SelectionModel& selection,
       VisualCursorDirection direction) OVERRIDE;
   virtual SelectionModel EdgeSelectionModel(
       VisualCursorDirection direction) OVERRIDE;
   virtual std::vector<Rect> GetSubstringBounds(size_t from, size_t to) OVERRIDE;
   virtual void SetSelectionModel(const SelectionModel& model) OVERRIDE;
   virtual bool IsCursorablePosition(size_t position) OVERRIDE;
   virtual void UpdateLayout() OVERRIDE;
   virtual void EnsureLayout() OVERRIDE;
-  virtual void DrawVisualText(Canvas* canvas) OVERRIDE;
+  virtual void DrawVisualText(CanvasSkia* canvas) OVERRIDE;
 
  private:
   virtual size_t IndexOfAdjacentGrapheme(
       size_t index,
       LogicalCursorDirection direction) OVERRIDE;
 
   void ItemizeLogicalText();
   void LayoutVisualText();
 
   // Returns a vector of linked fonts corresponding to |font|.
@@ skipping 26 matching lines @@
   scoped_array<int> logical_to_visual_;
 
   bool needs_layout_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderTextWin);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_RENDER_TEXT_WIN_H_