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 f7a7ff5d3e932d2bd113ffa9d67803e19ffb71b0..bee26511da58042f207331d4ba6658dde4111766 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
@@ -173,6 +173,8 @@ class CORE_EXPORT HTMLCanvasElement final
   // ContextLifecycleObserver and PageVisibilityObserver implementation
   void contextDestroyed(ExecutionContext*) override;
 
+  void finalizeFrame();
+
   // PageVisibilityObserver implementation
   void pageVisibilityChanged() override;
 
@@ -194,9 +196,8 @@ class CORE_EXPORT HTMLCanvasElement final
 
   // ImageBufferClient implementation
   void notifySurfaceInvalid() override;
-  bool isDirty() override { return !m_dirtyRect.isEmpty(); }
+  bool isDirty() { return !m_dirtyRect.isEmpty(); }
   void didDisableAcceleration() override;
-  void didFinalizeFrame() override;
   void restoreCanvasMatrixClipStack(SkCanvas*) const override;
 
   void doDeferredPaintInvalidation();