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

third_party/WebKit/LayoutTests/imported/wpt/pointerevents/pointerevent_support.js

 var All_Pointer_Events = [
         "pointerdown",
         "pointerup",
         "pointercancel",
         "pointermove",
         "pointerover",
         "pointerout",
         "pointerenter",
         "pointerleave",
         "gotpointercapture",
         "lostpointercapture"];
 
 // Check for conformance to PointerEvent interface
 // TA: 1.1, 1.2, 1.6, 1.7, 1.8, 1.9, 1.10, 1.11, 1.12, 1.13
-function check_PointerEvent(event) {
-    var pointerTestName = event.pointerType + ' ' + event.type;
+function check_PointerEvent(event, testNamePrefix) {
+    if (testNamePrefix === undefined)
+        testNamePrefix = "";
+    var pointerTestName = testNamePrefix + ' ' + event.pointerType + ' ' + event.type;
     test(function () {
-        assert_true(event instanceof PointerEvent, "event is a PointerEvent event");
+        assert_true(event instanceof event.target.ownerDocument.defaultView.PointerEvent, "event is a PointerEvent event");
     }, pointerTestName + " event is a PointerEvent event");
 
 
     // Check attributes for conformance to WebIDL:
     // * attribute exists
     // * has proper type
     // * if the attribute is "readonly", it cannot be changed
     // TA: 1.1, 1.2
     var idl_type_check = {
         "long": function (v) { return typeof v === "number" && Math.round(v) === v; },
@@ skipping 147 matching lines @@
 }
 
 function rPointerCapture(e) {
     try {
         captureButton.value = 'Set Capture';
         target0.releasePointerCapture(e.pointerId);
     }
     catch(e) {
     }
 }