Remove keyMirror in SpecPolicy (#7590)

As discussed in my RFC: https://www.facebook.com/groups/2003630259862046/permalink/2097088000516271/
(cherry picked from commit e3b2c6e650)

src/isomorphic/classic/class/ReactClass.js

@@ -18,7 +18,6 @@ var ReactNoopUpdateQueue = require('ReactNoopUpdateQueue');
 
 var emptyObject = require('emptyObject');
 var invariant = require('invariant');
-var keyMirror = require('keyMirror');
 var keyOf = require('keyOf');
 var warning = require('warning');
 
@@ -29,27 +28,26 @@ var MIXINS_KEY = keyOf({mixins: null});
 /**
  * Policies that describe methods in `ReactClassInterface`.
  */
-var SpecPolicy = keyMirror({
+type SpecPolicy =
   /**
    * These methods may be defined only once by the class specification or mixin.
    */
-  DEFINE_ONCE: null,
+  'DEFINE_ONCE' |
   /**
    * These methods may be defined by both the class specification and mixins.
    * Subsequent definitions will be chained. These methods must return void.
    */
-  DEFINE_MANY: null,
+  'DEFINE_MANY' |
   /**
    * These methods are overriding the base class.
    */
-  OVERRIDE_BASE: null,
+  'OVERRIDE_BASE' |
   /**
    * These methods are similar to DEFINE_MANY, except we assume they return
    * objects. We try to merge the keys of the return values of all the mixed in
    * functions. If there is a key conflict we throw.
    */
-  DEFINE_MANY_MERGED: null,
-});
+  'DEFINE_MANY_MERGED';
 
 
 var injectedMixins = [];
@@ -76,7 +74,7 @@ var injectedMixins = [];
  * @interface ReactClassInterface
  * @internal
  */
-var ReactClassInterface = {
+var ReactClassInterface: {[key: string]: SpecPolicy} = {
 
   /**
    * An array of Mixin objects to include when defining your component.
@@ -84,7 +82,7 @@ var ReactClassInterface = {
    * @type {array}
    * @optional
    */
-  mixins: SpecPolicy.DEFINE_MANY,
+  mixins: 'DEFINE_MANY',
 
   /**
    * An object containing properties and methods that should be defined on
@@ -93,7 +91,7 @@ var ReactClassInterface = {
    * @type {object}
    * @optional
    */
-  statics: SpecPolicy.DEFINE_MANY,
+  statics: 'DEFINE_MANY',
 
   /**
    * Definition of prop types for this component.
@@ -101,7 +99,7 @@ var ReactClassInterface = {
    * @type {object}
    * @optional
    */
-  propTypes: SpecPolicy.DEFINE_MANY,
+  propTypes: 'DEFINE_MANY',
 
   /**
    * Definition of context types for this component.
@@ -109,7 +107,7 @@ var ReactClassInterface = {
    * @type {object}
    * @optional
    */
-  contextTypes: SpecPolicy.DEFINE_MANY,
+  contextTypes: 'DEFINE_MANY',
 
   /**
    * Definition of context types this component sets for its children.
@@ -117,7 +115,7 @@ var ReactClassInterface = {
    * @type {object}
    * @optional
    */
-  childContextTypes: SpecPolicy.DEFINE_MANY,
+  childContextTypes: 'DEFINE_MANY',
 
   // ==== Definition methods ====
 
@@ -131,7 +129,7 @@ var ReactClassInterface = {
    * @return {object}
    * @optional
    */
-  getDefaultProps: SpecPolicy.DEFINE_MANY_MERGED,
+  getDefaultProps: 'DEFINE_MANY_MERGED',
 
   /**
    * Invoked once before the component is mounted. The return value will be used
@@ -147,13 +145,13 @@ var ReactClassInterface = {
    * @return {object}
    * @optional
    */
-  getInitialState: SpecPolicy.DEFINE_MANY_MERGED,
+  getInitialState: 'DEFINE_MANY_MERGED',
 
   /**
    * @return {object}
    * @optional
    */
-  getChildContext: SpecPolicy.DEFINE_MANY_MERGED,
+  getChildContext: 'DEFINE_MANY_MERGED',
 
   /**
    * Uses props from `this.props` and state from `this.state` to render the
@@ -171,7 +169,7 @@ var ReactClassInterface = {
    * @nosideeffects
    * @required
    */
-  render: SpecPolicy.DEFINE_ONCE,
+  render: 'DEFINE_ONCE',
 
 
 
@@ -184,7 +182,7 @@ var ReactClassInterface = {
    *
    * @optional
    */
-  componentWillMount: SpecPolicy.DEFINE_MANY,
+  componentWillMount: 'DEFINE_MANY',
 
   /**
    * Invoked when the component has been mounted and has a DOM representation.
@@ -196,7 +194,7 @@ var ReactClassInterface = {
    * @param {DOMElement} rootNode DOM element representing the component.
    * @optional
    */
-  componentDidMount: SpecPolicy.DEFINE_MANY,
+  componentDidMount: 'DEFINE_MANY',
 
   /**
    * Invoked before the component receives new props.
@@ -217,7 +215,7 @@ var ReactClassInterface = {
    * @param {object} nextProps
    * @optional
    */
-  componentWillReceiveProps: SpecPolicy.DEFINE_MANY,
+  componentWillReceiveProps: 'DEFINE_MANY',
 
   /**
    * Invoked while deciding if the component should be updated as a result of
@@ -239,7 +237,7 @@ var ReactClassInterface = {
    * @return {boolean} True if the component should update.
    * @optional
    */
-  shouldComponentUpdate: SpecPolicy.DEFINE_ONCE,
+  shouldComponentUpdate: 'DEFINE_ONCE',
 
   /**
    * Invoked when the component is about to update due to a transition from
@@ -256,7 +254,7 @@ var ReactClassInterface = {
    * @param {ReactReconcileTransaction} transaction
    * @optional
    */
-  componentWillUpdate: SpecPolicy.DEFINE_MANY,
+  componentWillUpdate: 'DEFINE_MANY',
 
   /**
    * Invoked when the component's DOM representation has been updated.
@@ -270,7 +268,7 @@ var ReactClassInterface = {
    * @param {DOMElement} rootNode DOM element representing the component.
    * @optional
    */
-  componentDidUpdate: SpecPolicy.DEFINE_MANY,
+  componentDidUpdate: 'DEFINE_MANY',
 
   /**
    * Invoked when the component is about to be removed from its parent and have
@@ -283,7 +281,7 @@ var ReactClassInterface = {
    *
    * @optional
    */
-  componentWillUnmount: SpecPolicy.DEFINE_MANY,
+  componentWillUnmount: 'DEFINE_MANY',
 
 
 
@@ -299,7 +297,7 @@ var ReactClassInterface = {
    * @internal
    * @overridable
    */
-  updateComponent: SpecPolicy.OVERRIDE_BASE,
+  updateComponent: 'OVERRIDE_BASE',
 
 };
 
@@ -414,7 +412,7 @@ function validateMethodOverride(isAlreadyDefined, name) {
   // Disallow overriding of base class methods unless explicitly allowed.
   if (ReactClassMixin.hasOwnProperty(name)) {
     invariant(
-      specPolicy === SpecPolicy.OVERRIDE_BASE,
+      specPolicy === 'OVERRIDE_BASE',
       'ReactClassInterface: You are attempting to override ' +
       '`%s` from your class specification. Ensure that your method names ' +
       'do not overlap with React methods.',
@@ -425,8 +423,8 @@ function validateMethodOverride(isAlreadyDefined, name) {
   // Disallow defining methods more than once unless explicitly allowed.
   if (isAlreadyDefined) {
     invariant(
-      specPolicy === SpecPolicy.DEFINE_MANY ||
-      specPolicy === SpecPolicy.DEFINE_MANY_MERGED,
+      specPolicy === 'DEFINE_MANY' ||
+      specPolicy === 'DEFINE_MANY_MERGED',
       'ReactClassInterface: You are attempting to define ' +
       '`%s` on your component more than once. This conflict may be due ' +
       'to a mixin.',
@@ -521,8 +519,8 @@ function mixSpecIntoComponent(Constructor, spec) {
           // These cases should already be caught by validateMethodOverride.
           invariant(
             isReactClassMethod && (
-              specPolicy === SpecPolicy.DEFINE_MANY_MERGED ||
-              specPolicy === SpecPolicy.DEFINE_MANY
+              specPolicy === 'DEFINE_MANY_MERGED' ||
+              specPolicy === 'DEFINE_MANY'
             ),
             'ReactClass: Unexpected spec policy %s for key %s ' +
             'when mixing in component specs.',
@@ -532,9 +530,9 @@ function mixSpecIntoComponent(Constructor, spec) {
 
           // For methods which are defined more than once, call the existing
           // methods before calling the new property, merging if appropriate.
-          if (specPolicy === SpecPolicy.DEFINE_MANY_MERGED) {
+          if (specPolicy === 'DEFINE_MANY_MERGED') {
             proto[name] = createMergedResultFunction(proto[name], property);
-          } else if (specPolicy === SpecPolicy.DEFINE_MANY) {
+          } else if (specPolicy === 'DEFINE_MANY') {
             proto[name] = createChainedFunction(proto[name], property);
           }
         } else {