Add closure-library externs for csp, and our own hack file for elemen…

…tal2

externs/browser/cspviolationobserver_externs.js

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+/**
+ * @license
+ * Copyright The Closure Library Authors.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+/**
+ * @fileoverview Externs used by cspviolationobserver.js that are not available
+ * in the open-source Closure compiler release. This file should be deleted
+ * once w3c_reporting_observer.js is available in open-source externs.
+ *
+ * @externs
+ */
+
+// TODO(user): Remove this file once w3c_reporting_observer.js is
+//     available in the open-source Closure compiler.
+
+/**
+ * https://w3c.github.io/reporting/#interface-reporting-observer
+ * @constructor
+ * @param {!ReportingObserverCallback} callback
+ * @param {!ReportingObserverOptions} opts
+ */
+function ReportingObserver2(callback, opts) {}
+/** @return {void} */
+ReportingObserver2.prototype.observe = function() {};
+/** @return {void} */
+ReportingObserver2.prototype.disconnect = function() {};
+/** @return {!Array<!Report>} */
+ReportingObserver2.prototype.takeRecords = function() {};
+
+/**
+ * @typedef {ReportingObserver2|ReportingObserver}
+ * @suppress {duplicate}
+ */
+var ReportingObserver;
+
+
+/**
+ * @typedef {!function(!Array<Report>, !ReportingObserver): void}
+ * @suppress {duplicate}
+ */
+var ReportingObserverCallback;
+
+
+/**
+ * @constructor
+ */
+function ReportingObserverOptions2() {}
+/** @type {undefined|!Array<string>} */
+ReportingObserverOptions2.prototype.types;
+/** @type {boolean} */
+ReportingObserverOptions2.prototype.buffered;
+
+/**
+ * @typedef {ReportingObserverOptions2|ReportingObserverOptions}
+ * @suppress {duplicate}
+ */
+var ReportingObserverOptions;
+
+
+/**
+ * @constructor
+ * @suppress {duplicate}
+ */
+function Report2() {}
+/** @type {string} */ Report2.prototype.type;
+/** @type {string} */ Report2.prototype.url;
+/** @type {?ReportBody} */ Report2.prototype.body;
+
+/**
+ * @typedef {Report2|Report}
+ * @suppress {duplicate}
+ */
+var Report;
+
+
+/**
+ * @constructor
+ */
+function ReportBody2() {}
+
+/**
+ * @typedef {ReportBody2|ReportBody2}
+ * @suppress {duplicate}
+ */
+var ReportBody;

externs/browser/elemental2-1.1.0-hack.js

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+/**
+ * @fileoverview Describes types present in elemental2 1.1.0 that are not in closure-compiler, since they aren't
+ * real browser types. Presently this only contains the `WebWorker` type which never existed as a browser type,
+ * but showed up in closure-compiler as a typo or early draft or something. As long as elemental2 1.1.0 is
+ * supported, we must keep this file in our closure-compiler fork.
+ *
+ * TODO Remove this once elemental2 1.1.0 is considered to be unsupported by j2cl - this day may not come soon,
+ * if ever, as it is a "stable" release.
+ *
+ * @externs
+ */
+
+/**
+ * @see http://dev.w3.org/html5/workers/
+ * @constructor
+ * @implements {EventTarget}
+ */
+function WebWorker() {}
+
+/** @override */
+WebWorker.prototype.addEventListener = function(type, listener, opt_options) {};
+
+/** @override */
+WebWorker.prototype.removeEventListener = function(
+    type, listener, opt_options) {};
+
+/** @override */
+WebWorker.prototype.dispatchEvent = function(evt) {};
+
+/**
+ * Stops the worker process
+ * @return {undefined}
+ */
+WebWorker.prototype.terminate = function() {};
+
+/**
+ * Posts a message to the worker thread.
+ * @param {string} message
+ * @return {undefined}
+ */
+WebWorker.prototype.postMessage = function(message) {};
+
+/**
+ * Sent when the worker thread posts a message to its creator.
+ * @type {?function(!MessageEvent<*>): void}
+ */
+WebWorker.prototype.onmessage;
+
+/**
+ * Sent when the worker thread encounters an error.
+ * @type {?function(!ErrorEvent): void}
+ */
+WebWorker.prototype.onerror;
+