Initial implementation of display list backed 2D canvases

Source/platform/graphics/ImageBufferSurface.cpp

Index: Source/platform/graphics/ImageBufferSurface.cpp
diff --git a/Source/platform/graphics/ImageBufferSurface.cpp b/Source/platform/graphics/ImageBufferSurface.cpp
index f45925cb38e8820d18693425741c9a29b0fa1433..d284fe757f8b9555d06e0a46d61cb648daeedc21 100644
--- a/Source/platform/graphics/ImageBufferSurface.cpp
+++ b/Source/platform/graphics/ImageBufferSurface.cpp
@@ -35,6 +35,7 @@
 #include "platform/graphics/ImageBuffer.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkDevice.h"
+#include "third_party/skia/include/core/SkPicture.h"
 
 namespace blink {
 
@@ -45,6 +46,11 @@ ImageBufferSurface::ImageBufferSurface(const IntSize& size, OpacityMode opacityM
     setIsHidden(false);
 }
 
+PassRefPtr<SkPicture> ImageBufferSurface::getPicture()
+{
+    return nullptr;
+}
+
 void ImageBufferSurface::clear()
 {
     // Clear the background transparent or opaque, as required. It would be nice if this wasn't
@@ -55,12 +61,14 @@ void ImageBufferSurface::clear()
             canvas()->drawARGB(255, 0, 0, 0, SkXfermode::kSrc_Mode);
         else
             canvas()->drawARGB(0, 0, 0, 0, SkXfermode::kClear_Mode);
+        didClearCanvas();
     }
 }
 
-const SkBitmap& ImageBufferSurface::bitmap() const
+const SkBitmap& ImageBufferSurface::bitmap()
 {
     ASSERT(canvas());
+    willReadback();
     return canvas()->getTopDevice()->accessBitmap(false);
 }