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

third_party/WebKit/Source/core/html/HTMLCanvasElement.h

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.h b/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
index 70ee8cbf1192033d64be2c193bc720e8f20377f5..4c9dfeb6afdd5197fd0c3e86a4d08c3aef77207b 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
@@ -170,6 +170,12 @@ class CORE_EXPORT HTMLCanvasElement final
 
   InsertionNotificationRequest insertedInto(ContainerNode*) override;
 
+  bool isDirty() { return !m_dirtyRect.isEmpty(); }
+
+  void doDeferredPaintInvalidation();
+
+  void finalizeFrame();
+
   // ContextLifecycleObserver and PageVisibilityObserver implementation
   void contextDestroyed(ExecutionContext*) override;
 
@@ -194,13 +200,9 @@ class CORE_EXPORT HTMLCanvasElement final
 
   // ImageBufferClient implementation
   void notifySurfaceInvalid() override;
-  bool isDirty() override { return !m_dirtyRect.isEmpty(); }
   void didDisableAcceleration() override;
-  void didFinalizeFrame() override;
   void restoreCanvasMatrixClipStack(PaintCanvas*) const override;
 
-  void doDeferredPaintInvalidation();
-
   // ImageBitmapSource implementation
   IntSize bitmapSourceSize() const override;
   ScriptPromise createImageBitmap(ScriptState*,