Allow ImageBitmap objects to be created from placeholder canvases.

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

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/frame/ImageBitmap.h"
 
 #include "core/html/HTMLCanvasElement.h"
 #include "core/html/HTMLVideoElement.h"
 #include "core/html/ImageData.h"
 #include "platform/graphics/skia/SkiaUtils.h"
@@ skipping 451 matching lines @@
   m_image = StaticBitmapImage::create(std::move(skiaImage));
   m_image->setOriginClean(
       !video->wouldTaintOrigin(document->getSecurityOrigin()));
   m_image->setPremultiplied(parsedOptions.premultiplyAlpha);
 }
 
 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))
     return;
 
   bool isPremultiplyAlphaReverted = false;
   if (!parsedOptions.premultiplyAlpha) {
     parsedOptions.premultiplyAlpha = true;
     isPremultiplyAlphaReverted = true;
   }
@@ skipping 375 matching lines @@
 void ImageBitmap::adjustDrawRects(FloatRect* srcRect,
                                   FloatRect* dstRect) const {}
 
 FloatSize ImageBitmap::elementSize(const FloatSize&) const {
   return FloatSize(width(), height());
 }
 
 DEFINE_TRACE(ImageBitmap) {}
 
 }  // namespace blink