Measure XPath usage

We currently don't know how common xpath usage
is in the wild, but we should.

Review URL: https://codereview.chromium.org/204003003

git-svn-id: svn://svn.chromium.org/blink/trunk@169510 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/frame/UseCounter.h

@@ -309,6 +309,9 @@ public:
         ElementAnimateKeyframeListEffectObjectTiming = 292,
         ElementAnimateKeyframeListEffectDoubleTiming = 293,
         ElementAnimateKeyframeListEffectNoTiming = 294,
+        DocumentXPathCreateExpression = 295,
+        DocumentXPathCreateNSResolver = 296,
+        DocumentXPathEvaluate = 297,
         // Add new features immediately above this line. Don't change assigned
         // numbers of any item, and don't reuse removed slots.
         NumberOfFeatures, // This enum value must be last.

third_party/WebKit/Source/core/xml/DocumentXPathEvaluator.idl

@@ -19,10 +19,10 @@
 
 partial interface Document {
     // DOM Level 3 XPath (XPathEvaluator interface)
-    [RaisesException] XPathExpression createExpression([Default=Undefined] optional DOMString expression,
+    [MeasureAs=DocumentXPathCreateExpression, RaisesException] XPathExpression createExpression([Default=Undefined] optional DOMString expression,
                                                        [Default=Undefined] optional XPathNSResolver resolver);
-    XPathNSResolver    createNSResolver(Node nodeResolver);
-    [Custom, RaisesException] XPathResult evaluate([Default=Undefined] optional DOMString expression,
+    [MeasureAs=DocumentXPathCreateNSResolver] XPathNSResolver    createNSResolver(Node nodeResolver);
+    [Custom, MeasureAs=DocumentXPathEvaluate, RaisesException] XPathResult evaluate([Default=Undefined] optional DOMString expression,
                                                    [Default=Undefined] optional Node contextNode,
                                                    [Default=Undefined] optional XPathNSResolver resolver,
                                                    [Default=Undefined] optional unsigned short type,