MD Settings: make chrome://[md-]settings/clearBrowserData URL work

chrome/browser/resources/settings/settings_main/settings_main_rendered.js

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+cr.define('settings.main', function() {
+  /** @type {!Promise} */
+  var promise;
+
+  return {
+    /** @return {!Promise} */
+    get rendered() {
+      return assert(promise, 'rendered promise must be set before accessing');
+    },
+
+    /** @param {!Promise} rendered */
+    set rendered(rendered) {
+      assert(!promise, 'settings.main.rendered should only be set once');

[michaelpg, 2016/06/29 22:46:52]

thanks for these asserts. I get scared by global promises that aren't
immediately set or can be set twice. Maybe we should even make this a pattern or
a part of PromiseResolver somehow.

[Dan Beam, 2016/06/29 23:12:24]

PromiseResolver already enforces this in some sense:
https://cs.chromium.org/chromium/src/ui/webui/resources/js/promise_resolver.j...

+      promise = rendered;
+    },
+  };
+});