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

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

Index: third_party/WebKit/Source/core/html/canvas/CanvasRenderingContext.cpp
diff --git a/third_party/WebKit/Source/core/html/canvas/CanvasRenderingContext.cpp b/third_party/WebKit/Source/core/html/canvas/CanvasRenderingContext.cpp
index 2ddfe27b909e4759d15e29fcb0e0e4f3733a9a88..0ff852d8634d8ba61173c0e18c5e2b6bac6fad1b 100644
--- a/third_party/WebKit/Source/core/html/canvas/CanvasRenderingContext.cpp
+++ b/third_party/WebKit/Source/core/html/canvas/CanvasRenderingContext.cpp
@@ -29,6 +29,7 @@
 #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";
@@ -108,6 +109,10 @@ SkColorType CanvasRenderingContext::colorType() const {
 }
 
 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
@@ -124,6 +129,24 @@ void CanvasRenderingContext::dispose() {
   }
 }
 
+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")