Add UMA metric to track usage of sending a mousedown to select elements.

third_party/WebKit/LayoutTests/imported/wpt/web-animations/testcommon.js

 /*
 Distributed under both the W3C Test Suite License [1] and the W3C
 3-clause BSD License [2]. To contribute to a W3C Test Suite, see the
 policies and contribution forms [3].
 
 [1] http://www.w3.org/Consortium/Legal/2008/04-testsuite-license
 [2] http://www.w3.org/Consortium/Legal/2008/03-bsd-license
 [3] http://www.w3.org/2004/10/27-testcases
  */
 
@@ skipping 10 matching lines @@
 // times based on their precision requirements.
 if (!window.assert_times_equal) {
   window.assert_times_equal = function(actual, expected, description) {
     assert_approx_equals(actual, expected, TIME_PRECISION, description);
   }
 }
 
 // creates div element, appends it to the document body and
 // removes the created element during test cleanup
 function createDiv(test, doc) {
+  return createElement(test, 'div', doc);
+}
+
+// creates element of given tagName, appends it to the document body and
+// removes the created element during test cleanup
+// if tagName is null or undefined, returns div element
+function createElement(test, tagName, doc) {
   if (!doc) {
     doc = document;
   }
-  var div = doc.createElement('div');
-  doc.body.appendChild(div);
+  var element = doc.createElement(tagName || 'div');
+  doc.body.appendChild(element);
   test.add_cleanup(function() {
-    div.remove();
+    element.remove();
   });
-  return div;
+  return element;
 }
 
 // Creates a style element with the specified rules, appends it to the document
 // head and removes the created element during test cleanup.
 // |rules| is an object. For example:
 // { '@keyframes anim': '' ,
 //   '.className': 'animation: anim 100s;' };
 // or
 // { '.className1::before': 'content: ""; width: 0px; transition: all 10s;',
 //   '.className2::before': 'width: 100px;' };
@@ skipping 94 matching lines @@
     function handleFrame() {
       if (--frameCount <= 0) {
         resolve();
       } else {
         window.requestAnimationFrame(handleFrame); // wait another frame
       }
     }
     window.requestAnimationFrame(handleFrame);
   });
 }