Improve fidelity of XHR progress events.

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 aa1fdff3c5446a3e1dc3bde4d227677e73d1638b..11ad7833d7d06c19d7fdc75b0aeac2fd803a94a1 100644
--- a/Source/core/xml/XMLHttpRequest.h
+++ b/Source/core/xml/XMLHttpRequest.h
@@ -184,11 +184,15 @@ private:
 
     void createRequest(ExceptionState&);
 
-    // Dispatches an event of the specified type to m_upload and
-    // m_progressEventThrottle.
-    void dispatchEventAndLoadEnd(const AtomicString&);
+    // Dispatches an event of the specified type to m_progressEventThrottle.
+    void dispatchEventAndLoadEnd(const AtomicString&, long long, long long);
 
-    void dispatchThrottledProgressEvent();
+    // Dispatches a response progress event to m_progressEventThrottle.
+    void dispatchThrottledProgressEvent(const AtomicString&, long long, long long);
+
+    // Dispatches a response progress event using values sampled from
+    // m_receivedLength and m_response.
+    void dispatchThrottledProgressEventSnapshot(const AtomicString&);
 
     // Does clean up common for all kind of didFail() call.
     void handleDidFailGeneric();
@@ -199,7 +203,7 @@ private:
     // Handles didFail() call for timeout.
     void handleDidTimeout();
 
-    void handleRequestError(ExceptionCode, const AtomicString&);
+    void handleRequestError(ExceptionCode, const AtomicString&, long long, long long);
 
     OwnPtr<XMLHttpRequestUpload> m_upload;