Abstract nsChangeHint_NonInherited_Hints into a function so that it accurately reports the reflow cases to all callers. (Bug 779968, patch 4) r=bzbarsky

This is in preparation for adding an additional caller.

nsChangeHint_NonInherited_Hints will be reintroduced in patch 6, but as
the maximum set of such hints rather than the minimal set, and with the
less confusing name nsChangeHint_Hints_NotHandledForDescendants.

layout/base/nsChangeHint.h

@@ -107,25 +107,10 @@ enum nsChangeHint {
    * has changed whether the frame is a container for fixed-pos or abs-pos
    * elements, but reframing is otherwise not needed.
    */
-  nsChangeHint_AddOrRemoveTransform = 0x4000,
+  nsChangeHint_AddOrRemoveTransform = 0x4000
 
-  /**
-   * We have an optimization when processing change hints which prevents
-   * us from visiting the descendants of a node when a hint on that node
-   * is being processed.  This optimization does not apply in some of the
-   * cases where applying a hint to an element does not necessarily result
-   * in the same hint being handled on the descendants.
-   *
-   * If you're adding such a hint, you should add your hint to this list.
-   */
-  nsChangeHint_NonInherited_Hints =
-    nsChangeHint_UpdateTransformLayer |
-    nsChangeHint_UpdateEffects |
-    nsChangeHint_UpdateOpacityLayer |
-    nsChangeHint_UpdateOverflow |
-    nsChangeHint_ChildrenOnlyTransform |
-    nsChangeHint_RecomputePosition |
-    nsChangeHint_AddOrRemoveTransform
+  // IMPORTANT NOTE: When adding new hints, consider whether you need to
+  // add them to NS_HintsNotHandledForDescendantsIn() below.
 };
 
 // Redefine these operators to return nothing. This will catch any use
@@ -164,6 +149,40 @@ inline bool NS_IsHintSubset(nsChangeHint aSubset, nsChangeHint aSuperSet) {
   return (aSubset & aSuperSet) == aSubset;
 }
 
+/**
+ * We have an optimization when processing change hints which prevents
+ * us from visiting the descendants of a node when a hint on that node
+ * is being processed.  This optimization does not apply in some of the
+ * cases where applying a hint to an element does not necessarily result
+ * in the same hint being handled on the descendants.
+ */
+inline nsChangeHint NS_HintsNotHandledForDescendantsIn(nsChangeHint aChangeHint) {
+  nsChangeHint result = nsChangeHint(aChangeHint & (
+    nsChangeHint_UpdateTransformLayer |
+    nsChangeHint_UpdateEffects |
+    nsChangeHint_UpdateOpacityLayer |
+    nsChangeHint_UpdateOverflow |
+    nsChangeHint_ChildrenOnlyTransform |
+    nsChangeHint_RecomputePosition |
+    nsChangeHint_AddOrRemoveTransform));
+
+  if (!NS_IsHintSubset(nsChangeHint_NeedDirtyReflow, aChangeHint) &&
+      NS_IsHintSubset(nsChangeHint_NeedReflow, aChangeHint)) {
+    // If NeedDirtyReflow is *not* set, then NeedReflow is a
+    // non-inherited hint.
+    NS_UpdateHint(result, nsChangeHint_NeedReflow);
+  }
+
+  if (!NS_IsHintSubset(nsChangeHint_ClearDescendantIntrinsics, aChangeHint) &&
+      NS_IsHintSubset(nsChangeHint_ClearAncestorIntrinsics, aChangeHint)) {
+    // If ClearDescendantIntrinsics is *not* set, then
+    // ClearAncestorIntrinsics is a non-inherited hint.
+    NS_UpdateHint(result, nsChangeHint_ClearAncestorIntrinsics);
+  }
+
+  return result;
+}
+
 // Redefine the old NS_STYLE_HINT constants in terms of the new hint structure
 #define NS_STYLE_HINT_NONE \
   nsChangeHint(0)

layout/base/nsFrameManager.cpp

@@ -1011,28 +1011,10 @@ nsFrameManager::ReResolveStyleContext(nsPresContext     *aPresContext,
                                       nsTArray<nsIContent*>& aVisibleKidsOfHiddenElement,
                                       TreeMatchContext &aTreeMatchContext)
 {
-  if (!NS_IsHintSubset(nsChangeHint_NeedDirtyReflow, aMinChange)) {
-    // 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);
-  }
-
   // We need to generate a new change list entry for every frame whose style
   // comparision returns one of these hints. These hints don't automatically
   // update all their descendant frames.
-  aMinChange = NS_SubtractHint(aMinChange, nsChangeHint_NonInherited_Hints);
+  aMinChange = NS_SubtractHint(aMinChange, NS_HintsNotHandledForDescendantsIn(aMinChange));
 
   // It would be nice if we could make stronger assertions here; they
   // would let us simplify the ?: expressions below setting |content|

layout/style/nsStyleContext.cpp

@@ -399,8 +399,7 @@ nsStyleContext::CalcStyleDifference(nsStyleContext* aOther)
              nsStyle##struct_::MaxDifference()),                              \
              "CalcDifference() returned bigger hint than MaxDifference()");   \
         NS_ASSERTION(nsStyle##struct_::ForceCompare() ||                      \
-             NS_IsHintSubset(nsStyle##struct_::MaxDifference(),               \
-                             nsChangeHint(~nsChangeHint_NonInherited_Hints)), \
+             NS_HintsNotHandledForDescendantsIn(nsStyle##struct_::MaxDifference()) == 0,  \
              "Structs that can return non-inherited hints must return true "  \
              "from ForceCompare");                                            \
         NS_UpdateHint(hint, this##struct_->CalcDifference(*other##struct_));  \