Use auto and Range-based loop interation in Source/core/dom/custom/

Source/core/dom/custom/CustomElementUpgradeCandidateMap.cpp

Index: Source/core/dom/custom/CustomElementUpgradeCandidateMap.cpp
diff --git a/Source/core/dom/custom/CustomElementUpgradeCandidateMap.cpp b/Source/core/dom/custom/CustomElementUpgradeCandidateMap.cpp
index 8241e7727c1d030841fa3d25541dc707a470c2cd..6850f6462a80177d4f05f2e7c4d0e3c39958035b 100644
--- a/Source/core/dom/custom/CustomElementUpgradeCandidateMap.cpp
+++ b/Source/core/dom/custom/CustomElementUpgradeCandidateMap.cpp
@@ -103,9 +103,9 @@ PassOwnPtrWillBeRawPtr<CustomElementUpgradeCandidateMap::ElementSet> CustomEleme
     if (!candidates)
         return nullptr;
 
-    for (ElementSet::const_iterator candidate = candidates->begin(); candidate != candidates->end(); ++candidate) {
-        unobserve(*candidate);
-        m_upgradeCandidates.remove(*candidate);
+    for (const auto& candidate : *candidates) {
+        unobserve(candidate);
+        m_upgradeCandidates.remove(candidate);
     }
     return candidates.release();
 }