Use downloadToFile option when XHR downloads a Blob

Source/core/xml/XMLHttpRequest.h

Index: Source/core/xml/XMLHttpRequest.h
diff --git a/Source/core/xml/XMLHttpRequest.h b/Source/core/xml/XMLHttpRequest.h
index 56fe38b59d7aff66bfece7e13f62cc97e466fca2..3416cbace30a9d1e09060af5c095c8039f356347 100644
--- a/Source/core/xml/XMLHttpRequest.h
+++ b/Source/core/xml/XMLHttpRequest.h
@@ -157,6 +157,9 @@ private:
     virtual void didSendData(unsigned long long bytesSent, unsigned long long totalBytesToBeSent);
     virtual void didReceiveResponse(unsigned long identifier, const ResourceResponse&);
     virtual void didReceiveData(const char* data, int dataLength);
+    // When "blob" is specified as the responseType attribute, didDownloadData
+    // is called instead of didReceiveData.
+    virtual void didDownloadData(int dataLength);
     virtual void didFinishLoading(unsigned long identifier, double finishTime);
     virtual void didFail(const ResourceError&);
     virtual void didFailRedirectCheck();
@@ -172,6 +175,7 @@ private:
     String getRequestHeader(const AtomicString& name) const;
     void setRequestHeaderInternal(const AtomicString& name, const String& value);
 
+    void trackProgress(int dataLength);
     // Changes m_state and dispatches a readyStateChange event if new m_state
     // value is different from last one.
     void changeState(State newState);