Use C++11 range-based loop for core/clipboard, core/dom and core/testing

Source/core/dom/Node.cpp

Index: Source/core/dom/Node.cpp
diff --git a/Source/core/dom/Node.cpp b/Source/core/dom/Node.cpp
index b6a41e05c0776e04a007a9613f98db44ba72ccca..72346477e6bcfd09c20402ede861f8ee9f1257e4 100644
--- a/Source/core/dom/Node.cpp
+++ b/Source/core/dom/Node.cpp
@@ -2031,8 +2031,8 @@ void Node::notifyMutationObserversNodeWillDetach()
         }
 
         if (WillBeHeapHashSet<RawPtrWillBeMember<MutationObserverRegistration>>* transientRegistry = node->transientMutationObserverRegistry()) {
-            for (WillBeHeapHashSet<RawPtrWillBeMember<MutationObserverRegistration>>::iterator iter = transientRegistry->begin(); iter != transientRegistry->end(); ++iter)
-                (*iter)->observedSubtreeNodeWillDetach(*this);
+            for (auto& registration : *transientRegistry)
+                registration->observedSubtreeNodeWillDetach(*this);
         }
     }
 }