Add permissions helper class to carry out promise based testing

LayoutTests/resources/permissions-helper.js

+// This file provides a PermissionsHelper object which can be used by
+// LayoutTests using testRunner to handle permissions. The methods in the object
+// return promises so can be used to write idiomatic, race-free code.
+//
+// The current available methods are:
+// - setPermission: given a permission name (known by testRunner) and a state,
+// it will set the permission to the specified state and resolve the promise
+// when done.
+// Example:
+// PermissionsHelper.setPermission('geolocation', 'prompt').then(runTest);
+"use strict";
+
+var PermissionsHelper = (function() {
+  function nameToObject(permissionName) {
+    switch (permissionName) {
+      case "midi":
+        return {name: "midi"};
+      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 permission name provided";
+    }
+  }
+
+  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);
+        });
+      });
+    }
+  }
+})();