Synchronize OffscreenCanvas content with the placeholder canvas

third_party/WebKit/Source/modules/canvas/HTMLCanvasElementModule.cpp

 // Copyright 2016 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 "modules/canvas/HTMLCanvasElementModule.h"
 
 #include "core/dom/DOMNodeIds.h"
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/offscreencanvas/OffscreenCanvas.h"
@@ skipping 47 matching lines @@
     HTMLCanvasElement& canvas,
     ExceptionState& exceptionState) {
   if (canvas.renderingContext()) {
     exceptionState.throwDOMException(
         InvalidStateError,
         "Cannot transfer control from a canvas that has a rendering context.");
     return nullptr;
   }
   OffscreenCanvas* offscreenCanvas =
       OffscreenCanvas::create(canvas.width(), canvas.height());
-  offscreenCanvas->setAssociatedCanvasId(DOMNodeIds::idForNode(&canvas));
+
+  int canvasId = DOMNodeIds::idForNode(&canvas);
+  offscreenCanvas->setPlaceholderCanvasId(canvasId);
+  canvas.registerPlaceholder(canvasId);
 
   CanvasSurfaceLayerBridge* bridge = canvas.surfaceLayerBridge();
   if (bridge) {
     // If a bridge exists, it means canvas.createSurfaceLayer() has been called
     // and its SurfaceId has been populated as well.
     offscreenCanvas->setSurfaceId(
         bridge->getSurfaceId().frame_sink_id().client_id(),
         bridge->getSurfaceId().frame_sink_id().sink_id(),
         bridge->getSurfaceId().local_frame_id().local_id(),
         bridge->getSurfaceId()
             .local_frame_id()
             .nonce()
             .GetHighForSerialization(),
         bridge->getSurfaceId()
             .local_frame_id()
             .nonce()
             .GetLowForSerialization());
   }
   return offscreenCanvas;
 }
 }