Bug 508900. Fix assertion due to us not unsetting all the bits we should unset. r=dbaron

layout/base/nsFrameManager.cpp

@@ -1080,6 +1080,10 @@ CaptureChange(nsStyleContext* aOldContext, nsStyleContext* aNewContext,
               nsChangeHint aChangeToAssume)
 {
   nsChangeHint ourChange = aOldContext->CalcStyleDifference(aNewContext);
+  NS_ASSERTION(!(ourChange & nsChangeHint_ReflowFrame) ||
+               (ourChange & nsChangeHint_NeedReflow),
+               "Reflow hint bits set without actually asking for a reflow");
+
   NS_UpdateHint(ourChange, aChangeToAssume);
   if (NS_UpdateHint(aMinChange, ourChange)) {
     aChangeList->AppendChange(aFrame, aContent, ourChange);
@@ -1103,14 +1107,22 @@ nsFrameManager::ReResolveStyleContext(nsPresContext     *aPresContext,
                                       nsChangeHint       aMinChange,
                                       PRBool             aFireAccessibilityEvents)
 {
-  // If aMinChange doesn't include nsChangeHint_NeedDirtyReflow, clear out the
-  // nsChangeHint_NeedReflow bit from it, so that we'll make sure to append a
-  // change to the list for ourselves if we need a reflow.  Need this because
-  // the parent may or may not actually end up reflowing us otherwise.  This
-  // works because any reflow hint will include nsChangeHint_NeedReflow, which
-  // will be missing from aMinChange.
   if (!NS_IsHintSubset(nsChangeHint_NeedDirtyReflow, aMinChange)) {
-    aMinChange = NS_SubtractHint(aMinChange, nsChangeHint_NeedReflow);
+    // If aMinChange doesn't include nsChangeHint_NeedDirtyReflow, clear out
+    // all the reflow change bits from it, so that we'll make sure to append a
+    // change to the list for ourselves if we need a reflow.  We need this
+    // because the parent may or may not actually end up reflowing us
+    // otherwise.
+    aMinChange = NS_SubtractHint(aMinChange, nsChangeHint_ReflowFrame);
+  } else if (!NS_IsHintSubset(nsChangeHint_ClearDescendantIntrinsics,
+                              aMinChange)) {
+    // If aMinChange doesn't include nsChangeHint_ClearDescendantIntrinsics,
+    // clear out the nsChangeHint_ClearAncestorIntrinsics flag, since it's
+    // possible that we had some random ancestor that cleared ancestor
+    // intrinsic widths, but we still need to clear intrinsic widths on frames
+    // that are our ancestors but its descendants.
+    aMinChange =
+      NS_SubtractHint(aMinChange, nsChangeHint_ClearAncestorIntrinsics);
   }
   
   // It would be nice if we could make stronger assertions here; they

layout/base/nsStyleChangeList.cpp

@@ -94,6 +94,9 @@ nsStyleChangeList::AppendChange(nsIFrame* aFrame, nsIContent* aContent, nsChange
                "must have content");
   NS_ASSERTION(!aContent || aContent->IsNodeOfType(nsINode::eELEMENT),
                "Shouldn't be trying to restyle non-elements directly");
+  NS_ASSERTION(!(aHint & nsChangeHint_ReflowFrame) ||
+               (aHint & nsChangeHint_NeedReflow),
+               "Reflow hint bits set without actually asking for a reflow");
 
   if ((0 < mCount) && (aHint & nsChangeHint_ReconstructFrame)) { // filter out all other changes for same content
     if (aContent) {