Recalc sibling styles for forward positional rules on mutations only.

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index 1b88ddbf87c87a51d523e8985ea2cfadeba4c3c7..862c4e4eb991419bf022b534515b98b661b843b4 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -1829,14 +1829,16 @@ void Element::checkForSiblingStyleChanges(bool finishedParsingCallback, Node* be
     if (!style || (needsStyleRecalc() && childrenAffectedByPositionalRules()))
         return;
 
-    // Forward positional selectors include the ~ selector, nth-child, nth-of-type, first-of-type and only-of-type.
+    // Forward positional selectors include nth-child, nth-of-type, first-of-type and only-of-type.
+    // The indirect adjacent selector is the ~ selector.
     // Backward positional selectors include nth-last-child, nth-last-of-type, last-of-type and only-of-type.
-    // We have to invalidate everything following the insertion point in the forward case, and everything before the insertion point in the
-    // backward case.
+    // We have to invalidate everything following the insertion point in the forward and indirect adjacent case,
+    // and everything before the insertion point in the backward case.
     // |afterChange| is 0 in the parser callback case, so we won't do any work for the forward case if we don't have to.
     // For performance reasons we just mark the parent node as changed, since we don't want to make childrenChanged O(n^2) by crawling all our kids
     // here. recalcStyle will then force a walk of the children when it sees that this has happened.
-    if ((childrenAffectedByForwardPositionalRules() && afterChange) || (childrenAffectedByBackwardPositionalRules() && beforeChange)) {
+    if (((childrenAffectedByForwardPositionalRules() || childrenAffectedByIndirectAdjacentRules()) && afterChange)
+        || (childrenAffectedByBackwardPositionalRules() && beforeChange)) {
         setNeedsStyleRecalc(SubtreeStyleChange);
         return;
     }
@@ -2542,6 +2544,11 @@ void Element::setChildrenAffectedByDirectAdjacentRules()
     ensureElementRareData().setChildrenAffectedByDirectAdjacentRules(true);
 }
 
+void Element::setChildrenAffectedByIndirectAdjacentRules()
+{
+    ensureElementRareData().setChildrenAffectedByIndirectAdjacentRules(true);
+}
+
 void Element::setChildrenAffectedByForwardPositionalRules()
 {
     ensureElementRareData().setChildrenAffectedByForwardPositionalRules(true);
@@ -2571,6 +2578,7 @@ bool Element::childrenSupportStyleSharing() const
         && !rareDataChildrenAffectedByFirstChildRules()
         && !rareDataChildrenAffectedByLastChildRules()
         && !rareDataChildrenAffectedByDirectAdjacentRules()
+        && !rareDataChildrenAffectedByIndirectAdjacentRules()
         && !rareDataChildrenAffectedByForwardPositionalRules()
         && !rareDataChildrenAffectedByBackwardPositionalRules();
 }
@@ -2623,6 +2631,12 @@ bool Element::rareDataChildrenAffectedByDirectAdjacentRules() const
     return elementRareData()->childrenAffectedByDirectAdjacentRules();
 }
 
+bool Element::rareDataChildrenAffectedByIndirectAdjacentRules() const
+{
+    ASSERT(hasRareData());
+    return elementRareData()->childrenAffectedByIndirectAdjacentRules();
+}
+
 bool Element::rareDataChildrenAffectedByForwardPositionalRules() const
 {
     ASSERT(hasRareData());