XHR: separate delayed progress event flushing from dispatching of new.

Source/core/xml/XMLHttpRequestProgressEventThrottle.h

Index: Source/core/xml/XMLHttpRequestProgressEventThrottle.h
diff --git a/Source/core/xml/XMLHttpRequestProgressEventThrottle.h b/Source/core/xml/XMLHttpRequestProgressEventThrottle.h
index 36eddc5ec41a4d32276f28e719bfa9dcd3f9afed..37cce7fc2451932d5495d4b1a1cb90ae332e84e6 100644
--- a/Source/core/xml/XMLHttpRequestProgressEventThrottle.h
+++ b/Source/core/xml/XMLHttpRequestProgressEventThrottle.h
@@ -38,6 +38,7 @@ class EventTarget;
 
 enum ProgressEventAction {
     DoNotFlushProgressEvent,
+    FlushDeferredProgressEvent,
     FlushProgressEvent
 };
 
@@ -61,7 +62,8 @@ private:
 
     virtual void fired();
     void dispatchDeferredEvents(Timer<XMLHttpRequestProgressEventThrottle>*);
-    void flushProgressEvent();
+    bool flushDeferredProgressEvent();
+    void deliverProgressEvent();
 
     bool hasEventToDispatch() const;