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

third_party/WebKit/Source/core/html/canvas/CanvasRenderingContext.h

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 14 matching lines @@
 
 #ifndef CanvasRenderingContext_h
 #define CanvasRenderingContext_h
 
 #include "core/CoreExport.h"
 #include "core/html/HTMLCanvasElement.h"
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/layout/HitTestCanvasResult.h"
 #include "core/offscreencanvas/OffscreenCanvas.h"
 #include "platform/graphics/ColorBehavior.h"
+#include "public/platform/WebThread.h"
 #include "third_party/skia/include/core/SkColorSpace.h"
 #include "third_party/skia/include/core/SkImageInfo.h"
 #include "wtf/HashSet.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/text/StringHash.h"
 
 namespace blink {
 
 class CanvasImageSource;
 class HTMLCanvasElement;
 class ImageData;
 class ImageBitmap;
 class WebLayer;
 
 enum CanvasColorSpace {
   kLegacyCanvasColorSpace,
   kSRGBCanvasColorSpace,
   kLinearRGBCanvasColorSpace,
   kRec2020CanvasColorSpace,
   kP3CanvasColorSpace,
 };
 
 class CORE_EXPORT CanvasRenderingContext
     : public GarbageCollectedFinalized<CanvasRenderingContext>,
-      public ScriptWrappable {
+      public ScriptWrappable,
+      public WebThread::TaskObserver {
   WTF_MAKE_NONCOPYABLE(CanvasRenderingContext);
   USING_PRE_FINALIZER(CanvasRenderingContext, dispose);
 
  public:
   virtual ~CanvasRenderingContext() {}
 
   // A Canvas can either be "2D" or "webgl" but never both. If you request a 2D
   // canvas and the existing context is already 2D, just return that. If the
   // existing context is WebGL, then destroy it before creating a new 2D
   // context. Vice versa when requesting a WebGL canvas. Requesting a context
@@ skipping 32 matching lines @@
   virtual ContextType getContextType() const = 0;
   virtual bool isAccelerated() const { return false; }
   virtual bool shouldAntialias() const { return false; }
   virtual void setIsHidden(bool) = 0;
   virtual bool isContextLost() const { return true; }
   virtual void setCanvasGetContextResult(RenderingContext&) { NOTREACHED(); };
   virtual void setOffscreenCanvasGetContextResult(OffscreenRenderingContext&) {
     NOTREACHED();
   }
   virtual bool isPaintable() const = 0;
+  virtual void didDraw(const SkIRect& dirtyRect);
 
   // Return true if the content is updated.
   virtual bool paintRenderingResultsToCanvas(SourceDrawingBuffer) {
     return false;
   }
 
   virtual WebLayer* platformLayer() const { return nullptr; }
 
   enum LostContextMode {
     NotLostContext,
 
     // Lost context occurred at the graphics system level.
     RealLostContext,
 
     // Lost context provoked by WEBGL_lose_context.
     WebGLLoseContextLostContext,
 
     // Lost context occurred due to internal implementation reasons.
     SyntheticLostContext,
   };
   virtual void loseContext(LostContextMode) {}
 
+  // WebThread::TaskObserver implementation
+  void didProcessTask() override;
+  void willProcessTask() final {}
+
   // Canvas2D-specific interface
   virtual bool is2d() const { return false; }
   virtual void restoreCanvasMatrixClipStack(PaintCanvas*) const {}
   virtual void reset() {}
   virtual void clearRect(double x, double y, double width, double height) {}
   virtual void didSetSurfaceSize() {}
   virtual void setShouldAntialias(bool) {}
   virtual unsigned hitRegionsCount() const { return 0; }
   virtual void setFont(const String&) {}
   virtual void styleDidChange(const ComputedStyle* oldStyle,
@@ skipping 48 matching lines @@
 
  private:
   void dispose();
 
   Member<HTMLCanvasElement> m_canvas;
   Member<OffscreenCanvas> m_offscreenCanvas;
   HashSet<String> m_cleanURLs;
   HashSet<String> m_dirtyURLs;
   CanvasColorSpace m_colorSpace;
   CanvasContextCreationAttributes m_creationAttributes;
+  bool m_finalizeFrameScheduled = false;
 };
 
 }  // namespace blink
 
 #endif