Fix RNTester Snapshot and Integration tests missing polyfills

Summary: Emily removed some magic that required InitializeCore for everything back in Sept/Oct. These tests have been broken for a long time, so it wasn't obvious that they broke.

Reviewed By: ejanzer

Differential Revision: D13601264

fbshipit-source-id: ea6ab7c8891207dad06cd062968d019a236cf8fc

IntegrationTests/IntegrationTestsApp.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+require('InitializeCore');
 const React = require('react');
 const ReactNative = require('react-native');
 const {

RNTester/js/RNTesterApp.ios.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+require('InitializeCore');
 const AsyncStorage = require('AsyncStorage');
 const BackHandler = require('BackHandler');
 const Linking = require('Linking');