Make stream captures work on canvases that are not in the DOM.

third_party/WebKit/Source/platform/graphics/ImageBuffer.cpp

 /*
  * Copyright (c) 2008, Google Inc. All rights reserved.
  * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
@@ skipping 132 matching lines @@
                               size_t rowBytes,
                               int x,
                               int y) {
   return m_surface->writePixels(info, pixels, rowBytes, x, y);
 }
 
 bool ImageBuffer::isSurfaceValid() const {
   return m_surface->isValid();
 }
 
-bool ImageBuffer::isDirty() {
-  return m_client ? m_client->isDirty() : false;
+void ImageBuffer::finalizeFrame() {
+  m_surface->finalizeFrame();
 }
 
-void ImageBuffer::didFinalizeFrame() {
-  if (m_client)
-    m_client->didFinalizeFrame();
-}
-
-void ImageBuffer::finalizeFrame(const FloatRect& dirtyRect) {
-  m_surface->finalizeFrame(dirtyRect);
-  didFinalizeFrame();

[xlai (Olivia), 2017/02/08 17:58:40]

Great works. The previous logic flow was a bit messy as HTMLCanvasElement calls
this function and this function routes back to
HTMLCanvasElement::didFinalizeFrame() via m_client.

[Justin Novosad, 2017/02/08 18:43:12]

Exactly. I got rid of the zig-zag flow we had before.

+void ImageBuffer::doPaintInvalidation(const FloatRect& dirtyRect) {
+  m_surface->doPaintInvalidation(dirtyRect);
 }
 
 bool ImageBuffer::restoreSurface() const {
   return m_surface->isValid() || m_surface->restore();
 }
 
 void ImageBuffer::notifySurfaceInvalid() {
   if (m_client)
     m_client->notifySurfaceInvalid();
 }
@@ skipping 422 matching lines @@
   DCHECK(MIMETypeRegistry::isSupportedImageMIMETypeForEncoding(mimeType));
 
   Vector<unsigned char> result;
   if (!encodeImage(mimeType, quality, &result))
     return "data:,";
 
   return "data:" + mimeType + ";base64," + base64Encode(result);
 }
 
 }  // namespace blink