Bug 1044584 - Fix incorrect computation of mUploadTransferred. r=bz

content/base/src/nsXMLHttpRequest.cpp

@@ -3592,11 +3592,13 @@ nsXMLHttpRequest::OnProgress(nsIRequest *aRequest, nsISupports *aContext, uint64
   // So, try to remove the headers, if possible.
   bool lengthComputable = (aProgressMax != UINT64_MAX);
   if (upload) {
-    mUploadTransferred = aProgress;
+    uint64_t loaded = aProgress;
     if (lengthComputable) {
-      mUploadTransferred = aProgressMax - mUploadTotal;
+      uint64_t headerSize = aProgressMax - mUploadTotal;
+      loaded -= headerSize;
     }
     mUploadLengthComputable = lengthComputable;
+    mUploadTransferred = loaded;
     mProgressSinceLastProgressEvent = true;
 
     MaybeDispatchProgressEvents(false);