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..d48f7e4fbb39b7539690bb71c0563b52d307fbf6 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/Deque.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/RefPtr.h"
 
@@ -18,6 +20,9 @@ namespace blink {
 
 class ImageBuffer;
 
+// The same with the default state stack size in SkCanvas
+#define INITIAL_STATE_STACK_SIZE 1

[zino, 2014/09/03 10:50:17]

Should we use WTF::Deque? I think it is better to use WTF::LinkedStack.
Also, I'm not sure if WTF::Deque<..., 1> is able to expand the internal vector.

[Sergey, 2014/09/04 10:26:50]

Junov, what do you think? I would probably agree with Jinho, since LinkedStack
does not move objects, when it has to allocate more memory. And it seems Deque
is mostly design for big capacities, while I don't expect that anyone would
write a web page with more then 5-10 canvas state saves...

+
 class PLATFORM_EXPORT RecordingImageBufferSurface : public ImageBufferSurface {
     WTF_MAKE_NONCOPYABLE(RecordingImageBufferSurface); WTF_MAKE_FAST_ALLOCATED;
 public:
@@ -34,11 +39,22 @@ public:
     virtual void setImageBuffer(ImageBuffer*) OVERRIDE;
 
 private:
+    struct StateRec {
+    public:

[zino, 2014/09/03 10:50:17]

Is this Blink coding rule?
If not so, I think this is unnecessary.

[Sergey, 2014/09/11 12:58:53]

Probably not required here at all.

+        SkMatrix m_ctm;
+        SkRect m_clip;

[zino, 2014/09/03 10:50:18]

If you use getDeviceClipBounds(), you should probably use SkIRect.

[Sergey, 2014/09/11 12:58:52]

Probably not required here at all.

+    };
+    typedef Deque<StateRec, INITIAL_STATE_STACK_SIZE> 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;