Introduce Node::containingTreeScope(), which asserts that the node's root is a tree scope

third_party/WebKit/Source/core/dom/Element.cpp

Index: third_party/WebKit/Source/core/dom/Element.cpp
diff --git a/third_party/WebKit/Source/core/dom/Element.cpp b/third_party/WebKit/Source/core/dom/Element.cpp
index fe8f945943988dc2dfd501ec228d51f66d6d92c7..9694d1407ad4c4e5844fc8192a7563917e211943 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -2209,7 +2209,7 @@ void Element::parseAttribute(const QualifiedName& name, const AtomicString&, con
         int tabindex = 0;
         if (value.isEmpty()) {
             clearTabIndexExplicitlyIfNeeded();
-            if (treeScope().adjustedFocusedElement() == this) {
+            if (isInTreeScope() && rootTreeScope().adjustedFocusedElement() == this) {

[esprehn, 2016/04/27 07:52:23]

Why do we need to add the check here? We do adjustedFocusedElement() == this in
many places, if that's too expensive then we should add a method to Element that
checks isInTreeScope for you.

[hayato, 2016/05/23 06:22:09]

Done.

Yeah, TreeScope::adjustedFocusedElement() could be expensive.
I introduced Element::adjustedFocusedElementInTreeScope(), and updated callers
of TreeScope::adjustedFocusedElement() to use that. That would be a small
performance gain.

                 // We might want to call blur(), but it's dangerous to dispatch
                 // events here.
                 document().setNeedsFocusedElementCheck();
@@ -2407,7 +2407,7 @@ void Element::updateFocusAppearance(SelectionBehaviorOnFocus selectionBehavior)
 void Element::blur()
 {
     cancelFocusAppearanceUpdate();
-    if (treeScope().adjustedFocusedElement() == this) {
+    if (isInTreeScope() && rootTreeScope().adjustedFocusedElement() == this) {
         Document& doc = document();
         if (doc.page())
             doc.page()->focusController().setFocusedElement(0, doc.frame());
@@ -3129,7 +3129,7 @@ inline void Element::updateId(const AtomicString& oldId, const AtomicString& new
     if (oldId == newId)
         return;
 
-    updateId(treeScope(), oldId, newId);
+    updateId(rootTreeScope(), oldId, newId);
 }
 
 inline void Element::updateId(TreeScope& scope, const AtomicString& oldId, const AtomicString& newId)