Bug 1168495 - Restrict updated region to fall within GTK window. r=jrmuizel

--HG--
extra : rebase_source : 4c34f469e4cb9b5afcabd336615181b3be0bd5de

widget/gtk/nsWindow.cpp

@@ -6168,6 +6168,10 @@ nsWindow::EndRemoteDrawingInRegion(DrawTarget* aDrawTarget, nsIntRegion& aInvali
       !mShmImage)
     return;
 
+  if (mThebesSurface) {
+    aInvalidRegion.AndWith(nsIntRect(nsIntPoint(0, 0), mThebesSurface->GetSize()));
+  }
+
   gint scale = GdkScaleFactor();
   if (scale != 1) {
     aInvalidRegion.ScaleInverseRoundOut(scale, scale);