correctly determine when the image has changed sizes to avoid causing unnecessary reflows. now comparing twips to twips instead of twips to pixels. part of fix for bug #15722 (r=evaughan).

layout/xul/base/src/nsTitledButtonFrame.cpp

@@ -387,11 +387,19 @@ nsTitledButtonFrame::UpdateImage(nsIPresContext&  aPresContext)
 
         if (mImageLoader.IsImageSizeKnown()) {
           nsIImage* image = mImageLoader.GetImage();
-          if (image && image->GetWidth() == mImageRect.width && image->GetHeight() == mImageRect.height) {
+          if ( image ) {
+            // imageLib stores width/height in pixels and we store it in twips. do the conversion
+            // before comparing.
+		    float p2t = 0.0;
+            aPresContext.GetScaledPixelsToTwips(&p2t);
+            int imageWidth = NSIntPixelsToTwips(image->GetWidth(), p2t);
+            int imageHeight = NSIntPixelsToTwips(image->GetHeight(), p2t);
+            if ( imageWidth == mImageRect.width && imageHeight == mImageRect.height ) {
               reflow = PR_FALSE;
               Invalidate(nsRect(0, 0, mRect.width, mRect.height), PR_FALSE);
             }
           }
+        } 
 
         if (reflow) {
           // Force a reflow when the image size isn't already known