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

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

 /*
  * 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 11 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "core/html/canvas/CanvasRenderingContext.h"
 
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/html/canvas/CanvasImageSource.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/weborigin/SecurityOrigin.h"
+#include "public/platform/Platform.h"
 
 const char* const kLinearRGBCanvasColorSpaceName = "linear-rgb";
 const char* const kSRGBCanvasColorSpaceName = "srgb";
 const char* const kLegacyCanvasColorSpaceName = "legacy-srgb";
 
 namespace blink {
 
 CanvasRenderingContext::CanvasRenderingContext(
     HTMLCanvasElement* canvas,
     OffscreenCanvas* offscreenCanvas,
@@ skipping 59 matching lines @@
 SkColorType CanvasRenderingContext::colorType() const {
   switch (m_colorSpace) {
     case kLinearRGBCanvasColorSpace:
       return kRGBA_F16_SkColorType;
     default:
       return kN32_SkColorType;
   }
 }
 
 void CanvasRenderingContext::dispose() {
+  if (m_finalizeFrameScheduled) {
+    Platform::current()->currentThread()->removeTaskObserver(this);
+  }
+
   // HTMLCanvasElement and CanvasRenderingContext have a circular reference.
   // When the pair is no longer reachable, their destruction order is non-
   // deterministic, so the first of the two to be destroyed needs to notify
   // the other in order to break the circular reference.  This is to avoid
   // an error when CanvasRenderingContext2D::didProcessTask() is invoked

[xlai (Olivia), 2017/01/27 22:23:25]

Update the comment.

[Justin Novosad, 2017/02/07 21:52:29]

Done.

   // after the HTMLCanvasElement is destroyed.
   if (canvas()) {
     canvas()->detachContext();
     m_canvas = nullptr;
   }
   if (offscreenCanvas()) {
     offscreenCanvas()->detachContext();
     m_offscreenCanvas = nullptr;
   }
 }
 
+void CanvasRenderingContext::didDraw(const SkIRect& dirtyRect) {
+  canvas()->didDraw(SkRect::Make(dirtyRect));
+  if (!m_finalizeFrameScheduled) {
+    m_finalizeFrameScheduled = true;
+    Platform::current()->currentThread()->addTaskObserver(this);
+  }
+}
+
+void CanvasRenderingContext::didProcessTask() {
+  Platform::current()->currentThread()->removeTaskObserver(this);
+  m_finalizeFrameScheduled = false;
+
+  if (!canvas())
+    return;
+
+  canvas()->finalizeFrame();

[xlai (Olivia), 2017/01/27 22:23:25]

Can you add a comment here explaining why you call this finalizeFrame?

[Justin Novosad, 2017/02/07 21:52:29]

Done.

+}
+
 CanvasRenderingContext::ContextType CanvasRenderingContext::contextTypeFromId(
     const String& id) {
   if (id == "2d")
     return Context2d;
   if (id == "experimental-webgl")
     return ContextExperimentalWebgl;
   if (id == "webgl")
     return ContextWebgl;
   if (id == "webgl2")
     return ContextWebgl2;
@@ skipping 40 matching lines @@
   }
   return taintOrigin;
 }
 
 DEFINE_TRACE(CanvasRenderingContext) {
   visitor->trace(m_canvas);
   visitor->trace(m_offscreenCanvas);
 }
 
 }  // namespace blink