Move Map/Set to allowed features of ES6 styleguide.

docs/es6_chromium.md

 <!-- Feature template markdown:
 ## Header
 
 **Usage Example:**
 
 ```js
 
 ```
 
 **Documentation:** [link]()
@@ skipping 92 matching lines @@
 previous discussion. If the list arrives at some consensus, send a codereview
 to change this file accordingly, linking to your discussion thread.
 
 > Some descriptions and Usage examples are from [kangax](https://kangax.github.io/compat-table/es6/)
 and [http://es6-features.org/](http://es6-features.org/)
 
 # Allowed Features
 
 The following features are allowed in Chromium development.
 
-## `=>` (Arrow Functions)
+## => (Arrow Functions)
 
 Arrow functions provide a concise syntax to create a function, and fix a number
 of difficulties with `this` (e.g. eliminating the need to write `const self =
 this`). Particularly useful for nested functions or callbacks.
 
 Prefer arrow functions over `.bind(this)`.
 
 Arrow functions have an implicit return when used without a body block.
 
 **Usage Example:**
@@ skipping 19 matching lines @@
 
 **Discussion Notes / Link to Thread:**
 
 **Note**: => does not work in iOS9.  Don't use it in code that runs on Chrome for
 iOS.  There's a presubmit that should warn you about this.
 
 [Discussion thread](https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/iJrC4PVSfoU)
 
 ---
 
-## `Promise`
+## Promise
 
 The Promise object is used for asynchronous computations. A Promise represents a
 value which may be available now, or in the future, or never.
 
 **Usage Example:**
 
 ```js
 /** @type {!Promise} */
 var fullyLoaded = new Promise(function(resolve) {
   function isLoaded() { return document.readyState == 'complete'; }
@@ skipping 53 matching lines @@
 
 **Discussion Notes / Link to Thread:**
 https://groups.google.com/a/chromium.org/d/msg/chromium-dev/S1h-0m2ohOw/jyaiMGDlCwAJ
 
 **Note**: Not fully supported in iOS9.  Don't use it in code that runs on Chrome
 for iOS, unless you can verify it works. TODO: Remove this note once support for
 iOS9 is dropped.
 
 ---
 
+## Map
+
+A simple key/value map in which any value (both objects and primitive values)
+may be used as either a key or a value.
+
+**Usage Example:**
+
+```js
+var map = new Map();
+map.size === 0;  // true
+map.get('foo');  // undefined
+
+var key = 54;
+map.set(key, 123);
+map.size === 1;  // true
+map.has(key);  // true
+map.get(key);  // 123
+
+map.delete(key);
+map.has(key);  // false
+map.size === 0;  // true
+```
+
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-map-objects)
+[link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)
+
+**Discussion Notes:** Feature already extensively used prior to creation of
+this document.
+
+---
+
+## Set
+
+An object that lets you store unique values of any type, whether primitive
+values or object references.
+
+**Usage Example:**
+
+```js
+var set = new Set();
+
+set.add(123);
+set.size();  // 1
+set.has(123);  // true
+
+set.add(123);
+set.size();  // 1
+```
+
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-set-objects)
+[link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set)
+
+**Discussion Notes:** Feature already extensively used prior to creation of
+this document.
+
+---
+
 # Banned Features
 
 The following features are banned for Chromium development.
 
 # Features To Be Discussed
 
 The following features are currently disallowed. See the top of this page on
 how to propose moving a feature from this list into the allowed or banned
 sections.
 
-## `let` (Block-Scoped Variables)
+## let (Block-Scoped Variables)
 
 `let` declares a variable within the scope of a block.  This differs from `var`,
 which uses function level scope.
 
 **Usage Example:**
 
 ```js
 // Scope.
 function varTest() {
   var x = 1;
@@ skipping 22 matching lines @@
   let b = 'mundo;  // TypeError Identifier 'b' has already been declared.
 }
 ```
 
 **Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-let-and-const-declarations)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
-## `const` (Block-Scoped Constants)
+## const (Block-Scoped Constants)
 
 Constants (also known as "immutable variables") are variables which cannot be
 re-assigned new content. Note that if the value is an object, the object itself
 is still mutable.
 
 Also note that in Chrome, `const` is block scoped like `let`.
 
 **Usage Example:**
 
 ```js
@@ skipping 321 matching lines @@
 Object.getOwnPropertyNames(obj);  // []
 Object.getOwnPropertySymbols(obj);  // [foo, bar]
 ```
 
 **Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-symbol-constructor)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
-## `for ...of` Loops
+## for...of Loops
 
 Convenient operator to iterate over all values in an iterable collection. This
 differs from `for ...in`, which iterates over all iterable properties.
 
 **Usage Example:**
 
 ```js
 // Given an iterable collection fibonacci numbers...
 for (var n of fibonacci) {
   console.log(n);  // 1, 1, 2, 3, ...
@@ skipping 141 matching lines @@
 }
 
 ```
 
 **Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-generator-function-definitions)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
-## `Map`
-
-A simple key/value map in which any value (both objects and primitive values)
-may be used as either a key or a value.
-
-**Usage Example:**
-
-```js
-var map = new Map();
-map.size === 0;  // true
-map.get('foo');  // undefined
-
-var key = {};
-map.set(key, 123);
-map.size === 1;  // true
-map.has(key);  // true
-map.get(key);  // 123
-
-map.delete(key);
-map.has(key);  // false
-map.size === 0;  // true
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-map-objects)
-[link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `Set`
-
-An object that lets you store unique values of any type, whether primitive
-values or object references.
-
-**Usage Example:**
-
-```js
-var set = new Set();
-
-set.add(123);
-set.size();  // 1
-set.has(123);  // true
-
-set.add(123);
-set.size();  // 1
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-set-objects)
-[link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `WeakMap`
+## WeakMap
 
 WeakMap does not prevent garbage collection if nothing else refers to an object
 within the collection.
 
 **Usage Example:**
 
 ```js
 var key = {};
 var weakmap = new WeakMap();
 
 weakmap.set(key, 123);
 
 weakmap.has(key) && weakmap.get(key) === 123;  // true
 ```
 
 **Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-weakmap-objects)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
-## `WeakSet`
+## WeakSet
 
 WeakSet does not prevent garbage collection if nothing else refers to an object
 within the collection.
 
 **Usage Example:**
 
 ```js
 var obj1 = {};
 var weakset = new WeakSet();
 
@@ skipping 21 matching lines @@
 new UInt8ClampedArray();
 // ... You get the idea. Click on the Documentation link below to see all.
 ```
 
 **Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-typedarray-objects)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
-## `Proxy`
+## Proxy
 
 Hooking into runtime-level object meta-operations.
 
 **Usage Example:**
 
 ```js
 var keyTracker = new Proxy({}, {
   keysCreated: 0,
 
   get (receiver, key) {
@@ skipping 11 matching lines @@
 keyTracker.key1;  // 'key already exists'
 keyTracker.key2;  // '2 keys created!'
 ```
 
 **Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-proxy-object-internal-methods-and-internal-slots)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
-## `Reflection`
+## Reflection
 
 Make calls corresponding to the object meta-operations.
 
 **Usage Example:**
 
 ```js
 let obj = {a: 1};
 Object.defineProperty(obj, 'b', {value: 2});
 obj[Symbol('c')] = 3;
 Reflect.ownKeys(obj);  // ['a', 'b', Symbol(c)]
@@ skipping 13 matching lines @@
 
 ```js
 // See Doc
 ```
 
 **Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-math)
 
 **Discussion Notes / Link to Thread:**
 
 ---