Transfer canvas state to the next frame with noticable restrictions.

Source/platform/graphics/RecordingImageBufferSurface.h

 // Copyright 2014 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 RecordingImageBufferSurface_h
 #define RecordingImageBufferSurface_h
 
 #include "platform/graphics/ImageBufferSurface.h"
 #include "public/platform/WebThread.h"
+#include "third_party/skia/include/core/SkCanvas.h"
+#include "wtf/LinkedStack.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/RefPtr.h"
 
 class SkPicture;
 class SkPictureRecorder;
 class RecordingImageBufferSurfaceTest;
 
 namespace blink {
 
 class ImageBuffer;
 
 class PLATFORM_EXPORT RecordingImageBufferSurface : public ImageBufferSurface {
     WTF_MAKE_NONCOPYABLE(RecordingImageBufferSurface); WTF_MAKE_FAST_ALLOCATED;
 public:
     RecordingImageBufferSurface(const IntSize&, OpacityMode = NonOpaque);
     virtual ~RecordingImageBufferSurface();
 
     // Implementation of ImageBufferSurface interfaces
     virtual SkCanvas* canvas() const OVERRIDE;
     virtual PassRefPtr<SkPicture> getPicture() OVERRIDE;
     virtual bool isValid() const OVERRIDE { return true; }
     virtual void willAccessPixels() OVERRIDE;
     virtual void finalizeFrame() OVERRIDE;
     virtual void didClearCanvas() OVERRIDE;
     virtual void setImageBuffer(ImageBuffer*) OVERRIDE;
 
 private:
+    struct StateRec {
+    public:
+        SkMatrix m_ctm;
+        // FIXME: handle transferring non-rectangular clip to the new frame, crbug.com/392614
+        SkIRect m_clip;
+    };
+    typedef LinkedStack<StateRec> StateStack;
     friend class ::RecordingImageBufferSurfaceTest; // for unit testing
     void fallBackToRasterCanvas();
     void initializeCurrentFrame();
     bool finalizeFrameInternal();
 
+    // saves current clip and transform matrix of canvas
+    bool saveState(SkCanvas*, StateStack*);
+    // we should make sure that we can transfer state in saveState
+    void setCurrentState(SkCanvas*, StateStack*);
+
     OwnPtr<SkPictureRecorder> m_currentFrame;
     RefPtr<SkPicture> m_previousFrame;
     OwnPtr<SkCanvas> m_rasterCanvas;
     ImageBuffer* m_imageBuffer;
     int m_initialSaveCount;
     bool m_frameWasCleared;
 };
 
 } // namespace blink
 
 #endif