Add OffscreenCanvas to ImageBitmapSource union typedef

third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h

Index: third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h
diff --git a/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h b/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h
index 5750fbce3146ca302d04f4241a8107a47c62aa81..7640b0b5a2a5d8be0578df046356d5a1f21473bd 100644
--- a/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h
+++ b/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.h
@@ -27,7 +27,8 @@ typedef OffscreenCanvasRenderingContext2DOrWebGLRenderingContextOrWebGL2Renderin
     OffscreenRenderingContext;
 
 class CORE_EXPORT OffscreenCanvas final : public EventTargetWithInlineData,
-                                          public CanvasImageSource {
+                                          public CanvasImageSource,
+                                          public ImageBitmapSource {
   DEFINE_WRAPPERTYPEINFO();
 
  public:
@@ -103,6 +104,14 @@ class CORE_EXPORT OffscreenCanvas final : public EventTargetWithInlineData,
     return m_executionContext.get();
   }
 
+  // ImageBitmapSource implementation
+  IntSize bitmapSourceSize() const final;
+  ScriptPromise createImageBitmap(ScriptState*,
+                                  EventTarget&,
+                                  Optional<IntRect>,
+                                  const ImageBitmapOptions&,
+                                  ExceptionState&) final;
+
   // CanvasImageSource implementation
   PassRefPtr<Image> getSourceImageForCanvas(SourceImageStatus*,
                                             AccelerationHint,