Devtools: [WIP] Implement enhanced devtools extension language APIs

Source/devtools/front_end/es6.js

 /*
  * Copyright 2014 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
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 /**
  * @param {string} description
  * @return {symbol}
  */
 function Symbol(description) {}
 
 /** @const {symbol} */
 Symbol.iterator;
 
+/**
+ * @param {string} name
+ * @return {symbol}
+ */
+Symbol.for;
+
 
 /**
  * @interface
  * @template VALUE
  */
 function Iterable() {}
 
 // TODO(johnlenz): remove this when the compiler understands "symbol" natively
 /**
  * @return {Iterator.<VALUE>}
@@ skipping 801 matching lines @@
  */
 Promise.prototype.then = function(opt_onFulfilled, opt_onRejected) {};
 
 
 /**
  * @param {function(*): RESULT} onRejected
  * @return {!Promise.<RESULT>}
  * @template RESULT
  */
 Promise.prototype.catch = function(onRejected) {};