Fix build bustage due to checkin for bug 294086. I'll get this reviewed post checkin.

layout/generic/nsFrameFrame.cpp

@@ -443,7 +443,8 @@ nsSubDocumentFrame::ComputeSize(nsIRenderingContext *aRenderingContext,
   nsIFrame* subDocRoot = ObtainIntrinsicSizeFrame();
   if (subDocRoot) {
     return nsLayoutUtils::ComputeSizeWithIntrinsicDimensions(
-                            aRenderingContext, this,
+                            aRenderingContext,
+                            const_cast<nsSubDocumentFrame*>(this),
                             subDocRoot->GetIntrinsicSize(),
                             subDocRoot->GetIntrinsicRatio(),
                             aCBSize, aMargin, aBorder, aPadding);