Bug 616884. Part 1. When setting the clip on windows on Linux don't return early if the clip hasn't ever been set before. r=roc a=roc

widget/src/gtk2/nsWindow.cpp

@@ -4597,8 +4597,12 @@ nsWindow::SetWindowClipRegion(const nsTArray<nsIntRect>& aRects,
         pixman_region32_intersect(&intersectRegion,
                                   &newRegion, &existingRegion);
 
-        if (pixman_region32_equal(&intersectRegion, &existingRegion))
+        // If mClipRects is null we haven't set a clip rect yet, so we
+        // need to set the clip even if it is equal.
+        if (mClipRects &&
+            pixman_region32_equal(&intersectRegion, &existingRegion)) {
             return;
+        }
 
         if (!pixman_region32_equal(&intersectRegion, &newRegion)) {
             GetIntRects(intersectRegion, &intersectRects);