Validate React.Fragment props without Map. (#12504)

Author: heikkilamarko

packages/react/src/ReactElementValidator.js

@@ -30,8 +30,6 @@ let propTypesMisspellWarningShown;
 let getDisplayName = () => {};
 let getStackAddendum = () => {};
 
-let VALID_FRAGMENT_PROPS;
-
 if (__DEV__) {
   currentlyValidatingElement = null;
 
@@ -65,8 +63,6 @@ if (__DEV__) {
     stack += ReactDebugCurrentFrame.getStackAddendum() || '';
     return stack;
   };
-
-  VALID_FRAGMENT_PROPS = new Map([['children', true], ['key', true]]);
 }
 
 function getDeclarationErrorAddendum() {
@@ -257,7 +253,7 @@ function validateFragmentProps(fragment) {
   const keys = Object.keys(fragment.props);
   for (let i = 0; i < keys.length; i++) {
     const key = keys[i];
-    if (!VALID_FRAGMENT_PROPS.has(key)) {
+    if (key !== 'children' && key !== 'key') {
       warning(
         false,
         'Invalid prop `%s` supplied to `React.Fragment`. ' +