Revert of Simplify CanvasAsyncBlobCreator by removing ContextObserver and related tests

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 b06280ed04dbc1ccd318f1906b125c82ba05920f..415355203cc247ac165ee6aeac6040fa066e5589 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.h
@@ -101,8 +101,8 @@
     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(BlobCallback*, const String& mimeType, const ScriptValue& qualityArgument, ExceptionState&);
-    void toBlob(BlobCallback* callback, const String& mimeType, ExceptionState& exceptionState) { return toBlob(callback, mimeType, ScriptValue(), exceptionState); }
+    void toBlob(ScriptState*, BlobCallback*, const String& mimeType, const ScriptValue& qualityArgument, ExceptionState&);
+    void toBlob(ScriptState* scriptState, BlobCallback* callback, const String& mimeType, ExceptionState& exceptionState) { return toBlob(scriptState, callback, mimeType, ScriptValue(), exceptionState); }
 
     // Used for canvas capture.
     void addListener(CanvasDrawListener*);