Bug 607494. Don't create frame construction items for content that has a primary frame. r=bzbarsky a=blocking-final+

layout/base/nsCSSFrameConstructor.cpp

@@ -5043,10 +5043,13 @@ nsCSSFrameConstructor::AddFrameConstructionItems(nsFrameConstructorState& aState
 
   // XXX the GetContent() != aContent check is needed due to bug 135040.
   // Remove it once that's fixed.  
-  NS_ASSERTION(!aContent->GetPrimaryFrame() ||
-    aContent->GetPrimaryFrame()->GetContent() != aContent ||
-    aState.mCreatingExtraFrames,
-    "asked to create frame construction item for a node that already has a frame");
+  if (aContent->GetPrimaryFrame() &&
+      aContent->GetPrimaryFrame()->GetContent() == aContent &&
+      !aState.mCreatingExtraFrames) {
+    NS_ERROR("asked to create frame construction item for a node that already "
+             "has a frame");
+    return;
+  }
 
   // don't create a whitespace frame if aParent doesn't want it
   if (!NeedFrameFor(aState, aParentFrame, aContent)) {