Allow CanvasSkia to bind to an existing SkCanvas.

ui/gfx/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 UI_GFX_CANVAS_H_
 #define UI_GFX_CANVAS_H_
 #pragma once
 
 #include <string>
 
 #include "base/string16.h"
 // TODO(beng): remove these includes when we no longer depend on SkTypes.
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkXfermode.h"
 #include "ui/base/ui_export.h"
 #include "ui/gfx/native_widget_types.h"
 
+class SkCanvas;
+
 namespace ui {
 class Transform;
 
 typedef unsigned int TextureID;
 }
 
 namespace gfx {
 
 class Brush;
 class CanvasSkia;
@@ skipping 197 matching lines @@
   virtual void Transform(const ui::Transform& transform) = 0;
 #endif
 
   // Create a texture ID that can be used for accelerated drawing.
   virtual ui::TextureID GetTextureID() = 0;
 
   // TODO(beng): remove this once we don't need to use any skia-specific methods
   //             through this interface.
   // A quick and dirty way to obtain the underlying SkCanvas.
   virtual CanvasSkia* AsCanvasSkia();
   virtual const CanvasSkia* AsCanvasSkia() const;

[Ben Goodger (Google), 2011/10/05 17:11:45]

Did anyone use this for anything other than to get a SkCanvas? Can we just
remove this?

[piman, 2011/10/05 17:31:29]

I wanted to get rid of it, but there's a dozen or so calls that need this to
access a method of CanvasSkia that isn't an override of Canvas. Some of them
probably could be made that way, but others probably don't (like ExtractBitmap,
that returns a SkBitmap&), so I didn't push it. We could.

+  virtual SkCanvas* GetSkCanvas();
+  virtual const SkCanvas* GetSkCanvas() const;
 };
 
 class UI_EXPORT CanvasPaint {
  public:
   virtual ~CanvasPaint() {}
 
   // Creates a canvas that paints to |view| when it is destroyed. The canvas is
   // sized to the client area of |view|.
   static CanvasPaint* CreateCanvasPaint(gfx::NativeView view);
 
   // Returns true if the canvas has an invalid rect that needs to be repainted.
   virtual bool IsValid() const = 0;
 
   // Returns the rectangle that is invalid.
   virtual gfx::Rect GetInvalidRect() const = 0;
 
   // Returns the underlying Canvas.
   virtual Canvas* AsCanvas() = 0;
 };
 
 }  // namespace gfx;
 
 #endif  // UI_GFX_CANVAS_H_