Add support for Element.getAttributeNames()

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 65a83f23f495d473434e00c38afb79a3d409491b..e5ec4443f9e0b5535712c0b257741e657c7c15c1 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -2824,6 +2824,18 @@ bool Element::SupportsSpatialNavigationFocus() const {
           HasEventListeners(EventTypeNames::focusout));
 }
 
+Vector<AtomicString> Element::getAttributeNames() const {
+  Vector<AtomicString> attributesVector;
+  if (!hasAttributes())
+    return attributesVector;
+
+  AttributeCollection attributes = element_data_->Attributes();
+  attributesVector.ReserveInitialCapacity(attributes.size());
+  for (const Attribute& attr : attributes)
+    attributesVector.UncheckedAppend(attr.GetName().ToString());
+  return attributesVector;
+}
+
 bool Element::IsFocusable() const {
   // Style cannot be cleared out for non-active documents, so in that case the
   // needsLayoutTreeUpdateForNode check is invalid.