[HTMLCanvasElement.toBlob] Default callback version without scheduler

Source/core/html/HTMLCanvasElement.h

Index: Source/core/html/HTMLCanvasElement.h
diff --git a/Source/core/html/HTMLCanvasElement.h b/Source/core/html/HTMLCanvasElement.h
index f5e8cc2f860aa4d33ec8fd6bb7873af2b475470b..7173957a4058858e351c7dfdc0b3cc0cc92042ce 100644
--- a/Source/core/html/HTMLCanvasElement.h
+++ b/Source/core/html/HTMLCanvasElement.h
@@ -33,6 +33,7 @@
 #include "core/CoreExport.h"
 #include "core/dom/Document.h"
 #include "core/dom/DocumentVisibilityObserver.h"
+#include "core/fileapi/FileCallback.h"
 #include "core/html/HTMLElement.h"
 #include "core/html/canvas/CanvasImageSource.h"
 #include "platform/geometry/FloatRect.h"
@@ -113,6 +114,9 @@ public:
     String toDataURL(const String& mimeType, const ScriptValue& qualityArgument, ExceptionState&) const;
     String toDataURL(const String& mimeType, ExceptionState& exceptionState) const { return toDataURL(mimeType, ScriptValue(), exceptionState); }
 
+    void toBlob(FileCallback*, const String& mimeType, const ScriptValue& qualityArgument, ExceptionState&) const;
+    void toBlob(FileCallback* callback, const String& mimeType, ExceptionState& exceptionState) { return toBlob(callback, mimeType, ScriptValue(), exceptionState); }

[Noel Gordon, 2015/08/28 08:53:47]

nit: if you removed this line, does chrome compile?  Not sure there are any
callers of this second variant of toBlob (or the similar toDataURL variant
either). We should remove them if they are dead-code.

[xlai (Olivia), 2015/08/28 19:54:19]

Haven't tried removing it and compile yet; I'll give a try later. 

But I don't think they are dead code. What if users call toBlob or toDataURL
functions without supplying any quality arguments? 

+
     // Used for rendering
     void didDraw(const FloatRect&);
     void notifyObserversCanvasChanged(const FloatRect&);