Skip child ShadowRoots when invalidation does not have boundary crossing rules

Source/core/css/invalidation/StyleInvalidator.cpp

Index: Source/core/css/invalidation/StyleInvalidator.cpp
diff --git a/Source/core/css/invalidation/StyleInvalidator.cpp b/Source/core/css/invalidation/StyleInvalidator.cpp
index 39fb027fdba4805885ac8874bede480d3cc688ce..3874c2b93e68f63610c8ad2889e925bec1a61e84 100644
--- a/Source/core/css/invalidation/StyleInvalidator.cpp
+++ b/Source/core/css/invalidation/StyleInvalidator.cpp
@@ -71,6 +71,8 @@ StyleInvalidator::~StyleInvalidator()
 void StyleInvalidator::RecursionData::pushInvalidationSet(const DescendantInvalidationSet& invalidationSet)
 {
     ASSERT(!m_wholeSubtreeInvalid);
+    if (invalidationSet.treeBoundaryCrossing())
+        m_treeBoundaryCrossing = true;
     if (invalidationSet.wholeSubtreeInvalid()) {
         m_wholeSubtreeInvalid = true;
         return;
@@ -115,14 +117,16 @@ bool StyleInvalidator::invalidateChildren(Element& element)
 {
     bool someChildrenNeedStyleRecalc = false;
     for (ShadowRoot* root = element.youngestShadowRoot(); root; root = root->olderShadowRoot()) {
-        for (Element* child = ElementTraversal::firstWithin(*root); child; child = ElementTraversal::nextSibling(*child)) {
+        if (!m_recursionData.treeBoundaryCrossing() && !root->childNeedsStyleInvalidation() && !root->needsStyleInvalidation())
+            continue;

[rune, 2014/05/30 21:02:45]

Just an idea for further improvements:

If treeBoundaryCrossing is false, and something in the shadow tree needs
invalidation, we can continue with an empty set of invalidation sets here. For
instance by introducing a start index in addition to invalidationSetsSize in
RecursionCheckpoint. I see now you mentioned something along those lines in the
description.

+        for (Element* child = ElementTraversal::firstChild(*root); child; child = ElementTraversal::nextSibling(*child)) {
             bool childRecalced = invalidate(*child);
             someChildrenNeedStyleRecalc = someChildrenNeedStyleRecalc || childRecalced;
         }
         root->clearChildNeedsStyleInvalidation();
         root->clearNeedsStyleInvalidation();
     }
-    for (Element* child = ElementTraversal::firstWithin(element); child; child = ElementTraversal::nextSibling(*child)) {
+    for (Element* child = ElementTraversal::firstChild(element); child; child = ElementTraversal::nextSibling(*child)) {
         bool childRecalced = invalidate(*child);
         someChildrenNeedStyleRecalc = someChildrenNeedStyleRecalc || childRecalced;
     }