Bug 515811. mPrevChild needs to be set on early exit from nsBlockFrame::ReflowBlockFrame. r=fantasai sr=dbaron

--HG--
extra : rebase_source : a0a457fa9348f48ac4f491610098f7488501faf7

layout/generic/nsBlockFrame.cpp

@@ -2955,6 +2955,7 @@ nsBlockFrame::ReflowBlockFrame(nsBlockReflowState& aState,
       if (!*aState.mReflowState.mDiscoveredClearance) {
         *aState.mReflowState.mDiscoveredClearance = frame;
       }
+      aState.mPrevChild = frame;
       // Exactly what we do now is flexible since we'll definitely be
       // reflowed.
       return NS_OK;