Add some Fakes for easier interaction snapshot testing

Summary:
`Fake` components are simplified so snapshots are stable and reliable, and references are exported
so that interactions like `onRefresh` and `onScroll` can be called manually. Currently there is just
one global export for each class, but we may change this in the future if we need to manage multiple
`Fake`s of the same type in one render tree.

Right now these must be installed explicitly, but I might move them into `__mocks__` folders if it
seems reasonable to make them defaults.

Reviewed By: cpojer

Differential Revision: D4318207

fbshipit-source-id: 62802353a98b09ca1c80804ef7201ea63091f94a

Libraries/CustomComponents/ListView/__mocks__/ListViewMock.js

@@ -0,0 +1,60 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+'use strict';
+
+const ListViewDataSource = require('ListViewDataSource');
+const React = require('React');
+const ScrollView = require('ScrollView');
+const StaticRenderer = require('StaticRenderer');
+const View = require('View');
+
+class ListViewMock extends React.Component {
+  static latestRef: ?ListViewMock;
+  static defaultProps = {
+    renderScrollComponent: (props) => <ScrollView {...props} />,
+  }
+  componentDidMount() {
+    ListViewMock.latestRef = this;
+  }
+  render() {
+    const {dataSource, renderFooter, renderHeader} = this.props;
+    const rows = [renderHeader && renderHeader()];
+    const allRowIDs = dataSource.rowIdentities;
+    for (let sectionIdx = 0; sectionIdx < allRowIDs.length; sectionIdx++) {
+      const sectionID = dataSource.sectionIdentities[sectionIdx];
+      const rowIDs = allRowIDs[sectionIdx];
+      for (let rowIdx = 0; rowIdx < rowIDs.length; rowIdx++) {
+        const rowID = rowIDs[rowIdx];
+        rows.push(
+          <StaticRenderer
+            key={rowID}
+            shouldUpdate={true}
+            render={this.props.renderRow.bind(
+              null,
+              dataSource.getRowData(sectionIdx, rowIdx),
+              sectionID,
+              rowID
+            )}
+          />
+        );
+      }
+    }
+    renderFooter && rows.push(renderFooter());
+    return (
+      <View>
+        {this.props.renderScrollComponent({children: rows})}
+      </View>
+    );
+  }
+  static DataSource = ListViewDataSource;
+}
+
+module.exports = ListViewMock;