Minor fixes to DOM Test Fixtures (facebook#11542)

- Fix broken React logo reference
- Always use React from the window.

Author: nhunzaker

fixtures/dom/public/react-logo.svg

@@ -1,5 +1,5 @@
-import React from 'react';
 import PropTypes from 'prop-types';
+const React = window.React;
 
 const propTypes = {
   title: PropTypes.node.isRequired,

fixtures/dom/src/components/FixtureSet.js

@@ -34,7 +34,7 @@ class Header extends React.Component {
         <div className="header__inner">
           <span className="header__logo">
             <img
-              src="https://reactjs.org/img/logo.svg"
+              src={process.env.PUBLIC_URL + '/react-logo.svg'}
               alt=""
               width="32"
               height="32"

fixtures/dom/src/components/Header.js

@@ -1,6 +1,5 @@
-import React from 'react';
-
 import Fixture from '../../Fixture';
+const React = window.React;
 
 class InputPlaceholderFixture extends React.Component {
   constructor(props, context) {

fixtures/dom/src/components/fixtures/input-change-events/InputPlaceholderFixture.js

@@ -1,6 +1,5 @@
-import React from 'react';
-
 import Fixture from '../../Fixture';
+const React = window.React;
 
 class RadioClickFixture extends React.Component {
   constructor(props, context) {

fixtures/dom/src/components/fixtures/input-change-events/RadioClickFixture.js

@@ -1,6 +1,5 @@
-import React from 'react';
-
 import Fixture from '../../Fixture';
+const React = window.React;
 
 class RadioGroupFixture extends React.Component {
   constructor(props, context) {

fixtures/dom/src/components/fixtures/input-change-events/RadioGroupFixture.js

@@ -1,6 +1,5 @@
-import React from 'react';
-
 import Fixture from '../../Fixture';
+const React = window.React;
 
 class RangeKeyboardFixture extends React.Component {
   constructor(props, context) {

fixtures/dom/src/components/fixtures/input-change-events/RangeKeyboardFixture.js

@@ -1,11 +1,10 @@
-import React from 'react';
-
 import FixtureSet from '../../FixtureSet';
 import TestCase from '../../TestCase';
 import RangeKeyboardFixture from './RangeKeyboardFixture';
 import RadioClickFixture from './RadioClickFixture';
 import RadioGroupFixture from './RadioGroupFixture';
 import InputPlaceholderFixture from './InputPlaceholderFixture';
+const React = window.React;
 
 class InputChangeEvents extends React.Component {
   render() {