[dom] support iterable<> NodeList

Source/core/html/HTMLCollection.cpp

Index: Source/core/html/HTMLCollection.cpp
diff --git a/Source/core/html/HTMLCollection.cpp b/Source/core/html/HTMLCollection.cpp
index e2b14857228b5d7d87725109a4810d8a238860a9..d79ba45b571fe0edea4dc97d0e5266e86c72dc07 100644
--- a/Source/core/html/HTMLCollection.cpp
+++ b/Source/core/html/HTMLCollection.cpp
@@ -40,6 +40,42 @@
 
 namespace blink {
 
+namespace {
+
+class HTMLCollectionIterationSource final : public ValueIterable<Element*>::IterationSource {
+public:
+    explicit HTMLCollectionIterationSource(HTMLCollection* collection)
+        : m_collection(collection)
+    {
+    }
+
+    bool next(ScriptState* scriptState, Element*& value, ExceptionState& exceptionState) override
+    {
+        if (m_index >= m_collection->length()) {
+            value = nullptr;
+            return false;
+        }
+        value = m_collection->item(m_index);
+        return true;
+    }
+
+    DEFINE_INLINE_VIRTUAL_TRACE()
+    {
+        visitor->trace(m_collection);
+        ValueIterable<Element*>::IterationSource::trace(visitor);
+    }
+
+private:
+    const RefPtrWillBeMember<HTMLCollection> m_collection;
+};
+
+} // namespace
+
+ValueIterable<Element*>::IterationSource* HTMLCollection::startIteration(ScriptState*, ExceptionState&)
+{
+    return new HTMLCollectionIterationSource(this);
+}
+
 using namespace HTMLNames;
 
 static bool shouldTypeOnlyIncludeDirectChildren(CollectionType type)