Transfer canvas state to the next frame with noticable restrictions.

Source/platform/graphics/RecordingImageBufferSurface.h

Index: Source/platform/graphics/RecordingImageBufferSurface.h
diff --git a/Source/platform/graphics/RecordingImageBufferSurface.h b/Source/platform/graphics/RecordingImageBufferSurface.h
index c8af6a045081ddfc38190d3bd03f27eb84842e20..0e4a7d032d499ae214db522a177759d636dea0ce 100644
--- a/Source/platform/graphics/RecordingImageBufferSurface.h
+++ b/Source/platform/graphics/RecordingImageBufferSurface.h
@@ -7,6 +7,8 @@
 
 #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"
 
@@ -34,11 +36,23 @@ public:
     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;