Replace createClass with external react-create-class dependency

Warns when using React.createClass for the first time.

Usages of createClass in tests have been converted to plain JavaScript
classes. Tests that rely on replaceState or isMounted use
updater.enqueueReplaceState and updater.isMounted.

mocks/ReactElementTestChild.js

@@ -13,10 +13,10 @@
 
 var React = require('React');
 
-var Child = React.createClass({
-  render: function() {
+class Child extends React.Component {
+  render() {
     return React.createElement('div');
-  },
-});
+  }
+}
 
 module.exports = Child;

mocks/ReactMockedComponentTestComponent.js

@@ -13,23 +13,18 @@
 
 var React = require('React');
 
-var ReactMockedComponentTestComponent = React.createClass({
-  getDefaultProps: function() {
-    return {bar: 'baz'};
-  },
+class ReactMockedComponentTestComponent extends React.Component {
+  state = {foo: 'bar'};
 
-  getInitialState: function() {
-    return {foo: 'bar'};
-  },
-
-  hasCustomMethod: function() {
+  hasCustomMethod() {
     return true;
-  },
+  }
 
-  render: function() {
+  render() {
     return <span />;
-  },
+  }
 
-});
+}
+ReactMockedComponentTestComponent.defaultProps = {bar: 'baz'};
 
 module.exports = ReactMockedComponentTestComponent;

package.json

@@ -69,6 +69,7 @@
     "merge-stream": "^1.0.0",
     "object-assign": "^4.1.1",
     "platform": "^1.1.0",
+    "react-create-class": "15.5.0-alpha.2",
     "run-sequence": "^1.1.4",
     "through2": "^2.0.0",
     "tmp": "~0.0.28",