diff --git a/externs/browser/html5.js b/externs/browser/html5.js
index baa70d61c69..863fb8379b1 100644
--- a/externs/browser/html5.js
+++ b/externs/browser/html5.js
@@ -6500,3 +6500,31 @@ ViewTransition.prototype.updateCallbackDone;
 
 /** @return {undefined} */
 ViewTransition.prototype.skipTransition = function() {};
+
+/**
+ * @record
+ * @extends {EventInit}
+ * @see https://html.spec.whatwg.org/multipage/interaction.html#toggleeventinit
+ */
+function ToggleEventInit() {}
+
+/** @type {undefined|string} */
+ToggleEventInit.prototype.newState;
+
+/** @type {undefined|string} */
+ToggleEventInit.prototype.oldState;
+
+/**
+ * @param {string} type
+ * @param {ToggleEventInit=} opt_eventInitDict
+ * @see https://html.spec.whatwg.org/multipage/interaction.html#toggleevent
+ * @constructor
+ * @extends {Event}
+ */
+function ToggleEvent(type, opt_eventInitDict) {}
+
+/** @const {string} */
+ToggleEvent.prototype.newState;
+
+/** @const {string} */
+ToggleEvent.prototype.oldState;
diff --git a/externs/browser/weblocksapi.js b/externs/browser/weblocksapi.js
new file mode 100644
index 00000000000..159e1581876
--- /dev/null
+++ b/externs/browser/weblocksapi.js
@@ -0,0 +1,116 @@
+/*
+ * Copyright 2018 The Closure Compiler Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * @fileoverview Definitions for objects in the Web Locks API. Details of the
+ * API are at:
+ * https://wicg.github.io/web-locks/
+ *
+ * @externs
+ * @author ohsnapitscolin@google.com (Colin Dunn)
+ */
+
+/**
+ * Possible values are "shared" and "exclusive".
+ * @typedef {string}
+ * [Web Locks API Spec](https://wicg.github.io/web-locks/#idl-index)
+ */
+var LockMode;
+
+
+/**
+ * @interface
+ * [Web Locks API Spec](https://wicg.github.io/web-locks/#idl-index)
+ */
+function Lock() {}
+
+/** @const {string} */
+Lock.prototype.name;
+
+/** @const {!LockMode} */
+Lock.prototype.mode;
+
+
+/**
+ * @typedef {{
+ *   name: string,
+ *   mode: !LockMode,
+ *   clientId: string
+ * }}
+ * [Web Locks API Spec](https://wicg.github.io/web-locks/#idl-index)
+ */
+var LockInfo;
+
+
+/**
+ * @typedef {{
+ *   mode: (!LockMode|undefined),
+ *   ifAvailable: (boolean|undefined),
+ *   steal: (boolean|undefined),
+ *   signal: (!AbortSignal|undefined)
+ * }}
+ * [Web Locks API Spec](https://wicg.github.io/web-locks/#idl-index)
+ */
+var LockOptions;
+
+
+/**
+ * @typedef {{
+ *   held: !Array<!LockInfo>,
+ *   pending: !Array<!LockInfo>
+ * }}
+ * [Web Locks API Spec](https://wicg.github.io/web-locks/#idl-index)
+ */
+var LockManagerSnapshot;
+
+
+/**
+ * @typedef {(function(?Lock) : !Promise<*>)}
+ * [Web Locks API Spec](https://wicg.github.io/web-locks/#idl-index)
+ */
+var LockGrantedCallback;
+
+
+/**
+ * @interface
+ * [Web Locks API Spec](https://wicg.github.io/web-locks/#idl-index)
+ */
+function LockManager() {}
+/**
+ * @param {string} name
+ * @param {(!LockOptions|!LockGrantedCallback)} optionsOrCallback
+ * @param {!LockGrantedCallback=} callback
+ * @return {!Promise<*>}
+ */
+LockManager.prototype.request = function(name, optionsOrCallback, callback) {};
+
+/**
+ * @return {!Promise<!LockManagerSnapshot>}
+ */
+LockManager.prototype.query = function() {};
+
+
+/**
+ * @type {!LockManager}
+ * [Web Locks API Spec](https://wicg.github.io/web-locks/#idl-index)
+ */
+Navigator.prototype.locks;
+
+
+/**
+ * @type {!LockManager}
+ * [Web Locks API Spec](https://wicg.github.io/web-locks/#idl-index)
+ */
+WorkerNavigator.prototype.locks;