update last continuation assertion to account for overflow container continuations b=399687 r+sr=roc a=beltzner

layout/base/nsFrameManager.cpp

@@ -59,6 +59,7 @@
 #include "prthread.h"
 #include "plhash.h"
 #include "nsPlaceholderFrame.h"
+#include "nsContainerFrame.h"
 #include "nsBlockFrame.h"
 #include "nsGkAtoms.h"
 #include "nsCSSAnonBoxes.h"
@@ -669,7 +670,9 @@ nsFrameManager::InsertFrames(nsIFrame*       aParentFrame,
                              nsIFrame*       aPrevFrame,
                              nsIFrame*       aFrameList)
 {
-  NS_PRECONDITION(!aPrevFrame || !aPrevFrame->GetNextContinuation(),
+  NS_PRECONDITION(!aPrevFrame || (!aPrevFrame->GetNextContinuation()
+                  || IS_TRUE_OVERFLOW_CONTAINER(aPrevFrame->GetNextContinuation()))
+                  && !IS_TRUE_OVERFLOW_CONTAINER(aPrevFrame),
                   "aPrevFrame must be the last continuation in its chain!");
 
   return aParentFrame->InsertFrames(aListName, aPrevFrame, aFrameList);