Bug 84123 Image information is shown on title bar only after image is completely loaded

call UpdateTitleAndCharset in OnStartContainer, that's the earliest time at
which we have the image dimensions.
r=varga sr=bzbarsky

content/html/document/src/nsImageDocument.cpp

@@ -384,6 +384,7 @@ nsImageDocument::OnStartContainer(imgIRequest* aRequest, imgIContainer* aImage)
   if (mImageResizingEnabled) {
     CheckOverflowing();
   }
+  UpdateTitleAndCharset();
 
   return NS_OK;
 }