Add APIs for dynamic display lists, using SkDrawable and SkPictureRecorder::endRecordingAsDrawable.

sky/engine/core/painting/PictureRecorder.cpp

Index: sky/engine/core/painting/PictureRecorder.cpp
diff --git a/sky/engine/core/painting/PictureRecorder.cpp b/sky/engine/core/painting/PictureRecorder.cpp
index ee6265a253ce4848a21f9b1c80f26f2a99249a0e..08cb42317ccb0330e9165eb29220b2712856e8ea 100644
--- a/sky/engine/core/painting/PictureRecorder.cpp
+++ b/sky/engine/core/painting/PictureRecorder.cpp
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "sky/engine/core/painting/Canvas.h"
+#include "sky/engine/core/painting/Drawable.h"
 #include "sky/engine/core/painting/Picture.h"
 #include "sky/engine/core/painting/PictureRecorder.h"
 
@@ -37,6 +38,17 @@ PassRefPtr<Picture> PictureRecorder::endRecording()
     return picture.release();
 }
 
+PassRefPtr<Drawable> PictureRecorder::endRecordingAsDrawable()
+{
+    if (!isRecording())
+        return nullptr;
+    RefPtr<Drawable> drawable = Drawable::create(
+        adoptRef(m_pictureRecorder->endRecordingAsDrawable()));
+    m_canvas->clearSkCanvas();
+    m_canvas = nullptr;
+    return drawable.release();
+}
+
 void PictureRecorder::set_canvas(PassRefPtr<Canvas> canvas) { m_canvas = canvas; }
 
 } // namespace blink