Decouple Canvas from DisplayList and map Picture and PictureRecorder more directly to their Skia co…

sky/engine/core/painting/Canvas.h

Index: sky/engine/core/painting/Canvas.h
diff --git a/sky/engine/core/painting/Canvas.h b/sky/engine/core/painting/Canvas.h
index abd325643ec8188ffcf6a0feb467d3ef19f0d020..a4327449bc4fd6f78992e631f846653ef0e5630a 100644
--- a/sky/engine/core/painting/Canvas.h
+++ b/sky/engine/core/painting/Canvas.h
@@ -15,21 +15,25 @@
 #include "sky/engine/tonic/float32_list.h"
 #include "sky/engine/wtf/PassRefPtr.h"
 #include "sky/engine/wtf/RefCounted.h"
+#include "third_party/skia/include/core/SkCanvas.h"
 
 namespace blink {
-class Element;
 class CanvasImage;
 
 class Canvas : public RefCounted<Canvas>, public DartWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    Canvas(const FloatSize& size);
-    ~Canvas() override;
+    static PassRefPtr<Canvas> create(SkCanvas* skCanvas) {
+        ASSERT(skCanvas);
+        return adoptRef(new Canvas(skCanvas));
+    }
+
+    static PassRefPtr<Canvas> create(PassRefPtr<Canvas> canvas) {
+        ASSERT(canvas);
+        return create(canvas->m_canvas);
+    }
 
-    // Width/Height define a culling rect which Skia may use for optimizing
-    // out draw calls issued outside the rect.
-    float width() const { return m_size.width(); }
-    float height() const { return m_size.height(); }
+    ~Canvas() override;
 
     void save();
     void saveLayer(const Rect& bounds, const Paint* paint = nullptr);
@@ -59,15 +63,16 @@ public:
                    const Paint* paint);
 
     SkCanvas* skCanvas() { return m_canvas; }
+    void clearSkCanvas() { m_canvas = nullptr; }

[abarth-chromium, 2015/06/20 00:50:29]

How does this mechanism work with the create(PassRefPtr<Canvas>) constructor? 
It seems like the picture recorder will call clearSkCanvas() only on the
original Canvas object, which means other Canvas objects that make a copy of the
same SkCanvas* will now have pointers off into unallocated memory.

+    bool isRecording() const { return m_canvas != nullptr; }

[abarth-chromium, 2015/06/20 00:50:29]

Does anyone call this function anymore?  If not, we should probably remove it.

 
 protected:
-    PassRefPtr<DisplayList> finishRecording();
-
-    bool isRecording() const { return m_canvas; }
+    Canvas(SkCanvas* skCanvas);

[abarth-chromium, 2015/06/20 00:50:29]

Please mark one-argument constructors explicit.

 
 private:
-    FloatSize m_size;
-    RefPtr<DisplayList> m_displayList;
+    // The SkCanvas is supplied by a call to SkPictureRecorder::beginRecording,
+    // which does not transfer ownership.  For this reason, we hold a raw
+    // pointer and manually set the SkCanvas to null in clearSkCanvas.
     SkCanvas* m_canvas;
 };