Allow ImageBitmap objects to be created from placeholder canvases.

third_party/WebKit/Source/core/frame/ImageBitmap.cpp

Index: third_party/WebKit/Source/core/frame/ImageBitmap.cpp
diff --git a/third_party/WebKit/Source/core/frame/ImageBitmap.cpp b/third_party/WebKit/Source/core/frame/ImageBitmap.cpp
index 585a6413355182680312eb3e2765569e5f6d0c8d..c1cb64a471998ea3f1508f3306a180c6237de77a 100644
--- a/third_party/WebKit/Source/core/frame/ImageBitmap.cpp
+++ b/third_party/WebKit/Source/core/frame/ImageBitmap.cpp
@@ -469,7 +469,11 @@ ImageBitmap::ImageBitmap(HTMLCanvasElement* canvas,
                          Optional<IntRect> cropRect,
                          const ImageBitmapOptions& options) {
   ASSERT(canvas->isPaintable());
-  RefPtr<Image> input = canvas->copiedImage(BackBuffer, PreferAcceleration);
+  RefPtr<Image> input;
+  if (canvas->placeholderFrame())
+    input = canvas->placeholderFrame();
+  else
+    input = canvas->copiedImage(BackBuffer, PreferAcceleration);
   ParsedOptions parsedOptions =
       parseOptions(options, cropRect, IntSize(input->width(), input->height()));
   if (dstBufferSizeHasOverflow(parsedOptions))