Make ElementShadow::youngestShadowRoot() return a reference

third_party/WebKit/Source/core/dom/shadow/ElementShadow.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 131 matching lines @@
     removeDetachedShadowRoots();
 #endif
 }
 
 ShadowRoot& ElementShadow::addShadowRoot(Element& shadowHost, ShadowRootType type)
 {
     EventDispatchForbiddenScope assertNoEventDispatch;
     ScriptForbiddenScope forbidScript;
 
     if (type == ShadowRootType::V0) {
-        if (!youngestShadowRoot()) {
+        if (m_shadowRoots.isEmpty()) {

[hayato, 2015/10/19 06:58:19]

Updated: Use m_shadowRoots.isEmpty() here because !m_shadowRoots.tails() is
confusing.

[kochi, 2015/10/19 07:02:03]

Acknowledged.

             shadowHost.willAddFirstAuthorShadowRoot();
-        } else if (youngestShadowRoot()->type() == ShadowRootType::UserAgent) {
+        } else if (m_shadowRoots.tail()->type() == ShadowRootType::UserAgent) {
             shadowHost.willAddFirstAuthorShadowRoot();
             UseCounter::countDeprecation(shadowHost.document(), UseCounter::ElementCreateShadowRootMultipleWithUserAgentShadowRoot);
         } else {
             UseCounter::countDeprecation(shadowHost.document(), UseCounter::ElementCreateShadowRootMultiple);
         }
     } else if (type == ShadowRootType::Open || type == ShadowRootType::Closed) {
         shadowHost.willAddFirstAuthorShadowRoot();
     }
 
-    for (ShadowRoot* root = youngestShadowRoot(); root; root = root->olderShadowRoot())
+    for (ShadowRoot* root = m_shadowRoots.tail(); root; root = root->olderShadowRoot())

[kochi, 2015/10/19 07:02:03]

Should this be m_shadowRoots.head() instead of m_shadowRoots.tail()?

If this is m_shadowRoots.tail(), only the tail (oldest) shadow root will be
iterated in this loop, right?

[hayato, 2015/10/19 07:12:11]

Done. Nice catch!

         root->lazyReattachIfAttached();
 
     RefPtrWillBeRawPtr<ShadowRoot> shadowRoot = ShadowRoot::create(shadowHost.document(), type);
     shadowRoot->setParentOrShadowHostNode(&shadowHost);
     shadowRoot->setParentTreeScope(shadowHost.treeScope());
     m_shadowRoots.push(shadowRoot.get());
     setNeedsDistributionRecalc();
 
     shadowRoot->insertedInto(&shadowHost);
     shadowHost.setChildNeedsStyleRecalc();
@@ skipping 21 matching lines @@
         oldRoot->setNext(0);
     }
 }
 #endif
 
 void ElementShadow::attach(const Node::AttachContext& context)
 {
     Node::AttachContext childrenContext(context);
     childrenContext.resolvedStyle = 0;
 
-    for (ShadowRoot* root = youngestShadowRoot(); root; root = root->olderShadowRoot()) {
+    for (ShadowRoot* root = &youngestShadowRoot(); root; root = root->olderShadowRoot()) {
         if (root->needsAttach())
             root->attach(childrenContext);
     }
 }
 
 void ElementShadow::detach(const Node::AttachContext& context)
 {
     Node::AttachContext childrenContext(context);
     childrenContext.resolvedStyle = 0;
 
-    for (ShadowRoot* root = youngestShadowRoot(); root; root = root->olderShadowRoot())
+    for (ShadowRoot* root = &youngestShadowRoot(); root; root = root->olderShadowRoot())
         root->detach(childrenContext);
 }
 
 void ElementShadow::setNeedsDistributionRecalc()
 {
     if (m_needsDistributionRecalc)
         return;
     m_needsDistributionRecalc = true;
     host()->markAncestorsWithChildNeedsDistributionRecalc();
     clearDistribution();
 }
 
 bool ElementShadow::hasSameStyles(const ElementShadow* other) const
 {
-    ShadowRoot* root = youngestShadowRoot();
-    ShadowRoot* otherRoot = other->youngestShadowRoot();
+    ShadowRoot* root = &youngestShadowRoot();
+    ShadowRoot* otherRoot = &other->youngestShadowRoot();
     while (root || otherRoot) {
         if (!root || !otherRoot)
             return false;
 
         StyleSheetList* list = root->styleSheets();
         StyleSheetList* otherList = otherRoot->styleSheets();
 
         if (list->length() != otherList->length())
             return false;
 
@@ skipping 29 matching lines @@
     return it == m_nodeToInsertionPoints.end() ? nullptr : &it->value;
 #endif
 }
 
 void ElementShadow::distribute()
 {
     host()->setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::Shadow));
     WillBeHeapVector<RawPtrWillBeMember<HTMLShadowElement>, 32> shadowInsertionPoints;
     DistributionPool pool(*host());
 
-    for (ShadowRoot* root = youngestShadowRoot(); root; root = root->olderShadowRoot()) {
+    for (ShadowRoot* root = &youngestShadowRoot(); root; root = root->olderShadowRoot()) {
         HTMLShadowElement* shadowInsertionPoint = 0;
         const WillBeHeapVector<RefPtrWillBeMember<InsertionPoint>>& insertionPoints = root->descendantInsertionPoints();
         for (size_t i = 0; i < insertionPoints.size(); ++i) {
             InsertionPoint* point = insertionPoints[i].get();
             if (!point->isActive())
                 continue;
             if (isHTMLShadowElement(*point)) {
                 ASSERT(!shadowInsertionPoint);
                 shadowInsertionPoint = toHTMLShadowElement(point);
                 shadowInsertionPoints.append(shadowInsertionPoint);
@@ skipping 71 matching lines @@
             break;
         shadow->setNeedsSelectFeatureSet();
     }
     setNeedsDistributionRecalc();
 }
 
 void ElementShadow::clearDistribution()
 {
     m_nodeToInsertionPoints.clear();
 
-    for (ShadowRoot* root = youngestShadowRoot(); root; root = root->olderShadowRoot())
+    for (ShadowRoot* root = &youngestShadowRoot(); root; root = root->olderShadowRoot())
         root->setShadowInsertionPointOfYoungerShadowRoot(nullptr);
 }
 
 DEFINE_TRACE(ElementShadow)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_nodeToInsertionPoints);
     visitor->trace(m_selectFeatures);
     // Shadow roots are linked with previous and next pointers which are traced.
     // It is therefore enough to trace one of the shadow roots here and the
     // rest will be traced from there.
     visitor->trace(m_shadowRoots.head());
 #endif
 }
 
 } // namespace