Add a UseCounter for when xml:base takes effect in Element.baseURI

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index bbeda432053a4e4191fe25cf66ad145ba8cfee27..2e663af766630c0cf0857f530902a5e5d913ca64 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -1212,6 +1212,9 @@ const AtomicString& Element::locateNamespacePrefix(const AtomicString& namespace
 KURL Element::baseURI() const
 {
     const AtomicString& baseAttribute = fastGetAttribute(baseAttr);
+    if (!baseAttribute.isEmpty())
+        UseCounter::count(document(), UseCounter::ElementBaseURIFromXMLBase);
+
     KURL base(KURL(), baseAttribute);
     if (!base.protocol().isEmpty())
         return base;