Fix display list canvas not rendering correctly on high dpi displays

Source/platform/graphics/ImageBuffer.cpp

Index: Source/platform/graphics/ImageBuffer.cpp
diff --git a/Source/platform/graphics/ImageBuffer.cpp b/Source/platform/graphics/ImageBuffer.cpp
index 384d3b15d003b668f120d8c0366424edd83989b2..0208cd84d96c0704046c81bd9d415b0ede452801 100644
--- a/Source/platform/graphics/ImageBuffer.cpp
+++ b/Source/platform/graphics/ImageBuffer.cpp
@@ -267,7 +267,7 @@ void ImageBuffer::draw(GraphicsContext* context, const FloatRect& destRect, cons
     FloatRect srcRect = srcPtr ? *srcPtr : FloatRect(FloatPoint(), size());
     RefPtr<SkPicture> picture = m_surface->getPicture();

[Stephen White, 2014/12/12 22:14:12]

IWBN if the SkPicture-related stuff could all live in the surface, if possible,
and not be exposed at the ImageBuffer level.

Maybe we could have a draw(GraphicsContext* context, ...) virtual on
ImageBufferSurface? Just a thought.

[Justin Novosad, 2014/12/12 22:31:51]

Acknowledged.

     if (picture) {
-        context->drawPicture(picture.get(), destRect, srcRect, op, blendMode);
+        context->compositePicture(picture.get(), destRect, srcRect, op, blendMode);
         return;
     }