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

third_party/WebKit/LayoutTests/imported/wpt/common/get-host-info.sub.js

+function get_host_info() {
+
+  var HTTP_PORT = '{{ports[http][0]}}';
+  var HTTP_PORT2 = '{{ports[http][1]}}';
+  var HTTPS_PORT = '{{ports[https][0]}}';
+  var ORIGINAL_HOST = '{{host}}';
+  var REMOTE_HOST = (ORIGINAL_HOST === 'localhost') ? '127.0.0.1' : ('www1.' + ORIGINAL_HOST);
+
+  return {
+    HTTP_PORT: HTTP_PORT,
+    HTTP_PORT2: HTTP_PORT2,
+    HTTPS_PORT: HTTPS_PORT,
+    ORIGINAL_HOST: ORIGINAL_HOST,
+    REMOTE_HOST: REMOTE_HOST,
+
+    HTTP_ORIGIN: 'http://' + ORIGINAL_HOST + ':' + HTTP_PORT,
+    HTTPS_ORIGIN: 'https://' + ORIGINAL_HOST + ':' + HTTPS_PORT,
+    HTTPS_ORIGIN_WITH_CREDS: 'https://foo:bar@' + ORIGINAL_HOST + ':' + HTTPS_PORT,
+    HTTP_ORIGIN_WITH_DIFFERENT_PORT: 'http://' + ORIGINAL_HOST + ':' + HTTP_PORT2,
+    HTTP_REMOTE_ORIGIN: 'http://' + REMOTE_HOST + ':' + HTTP_PORT,
+    HTTP_REMOTE_ORIGIN_WITH_DIFFERENT_PORT: 'http://' + REMOTE_HOST + ':' + HTTP_PORT2,
+    HTTPS_REMOTE_ORIGIN: 'https://' + REMOTE_HOST + ':' + HTTPS_PORT,
+    HTTPS_REMOTE_ORIGIN_WITH_CREDS: 'https://foo:bar@' + REMOTE_HOST + ':' + HTTPS_PORT,
+  };
+}