Add permissions helper class to carry out promise based testing

LayoutTests/resources/permissions-helper.js

+var PermissionsHelper = (function() {
+  function nameToObject(permissionName) {
+    switch (permissionName) {
+      case "midi":
+        return {name: "midi"}

[mlamouri (slow - plz ping), 2015/08/22 10:19:29]

nit: add ;

same for all the following return statements.

Maybe you can add "use strict;" at the beginning of the file to prevent that
kind of mistakes?

[Lalit Maganti, 2015/08/24 09:18:23]

Done.

+      case "midi-sysex":
+        return {name: "midi", sysex: true}
+      case "push-messaging":
+        return {name: "push", userVisibleOnly: true}
+      case "notifications":
+        return {name: "notifications"}
+      case "geolocation":
+        return {name: "geolocation"}
+      default:
+        throw "Invalid "

[mlamouri (slow - plz ping), 2015/08/22 10:19:29]

nit: could you throw something that would be more helpful to the caller? :)

[Lalit Maganti, 2015/08/24 09:18:23]

I really shouldn't write CLs late on Friday :)

Done.

+    }
+  }
+
+  return {
+    setPermission: function(name, state) {
+      return new Promise(function(resolver, reject) {
+        navigator.permissions.query(nameToObject(name)).then(function(result) {
+            if (result.state == state) {
+                resolver()
+                return;
+            }
+
+            result.onchange = function() {
+                result.onchange = null;
+                resolver();
+            };
+
+            testRunner.setPermission(name, state, location.origin, location.origin);
+        });
+      });
+    }
+  }
+})();