Display platform-specific examples

Summary:
Rebased https://github.com/facebook/react-native/pull/7048

Sending a new PR to check that tests pass.

After adding simulator examples, it appears that some don't show up, ex:
http://facebook.github.io/react-native/docs/text.html#content

This is due to the fact that these examples are split into two platform-specific files. For this reason, the example code isn't being shown. The examples are also missing for TextInput.

**Test plan**

`cd website; npm install; npm start`

![screen shot 2016-05-05 at 12 25 41 pm](https://cloud.githubusercontent.com/assets/346214/15042571/08ee77e8-12bd-11e6-98a6-967dc5fefa07.png)

![screen shot 2016-05-05 at 12 25 20 pm](https://cloud.githubusercontent.com/assets/346214/15042573/119778f4-12bd-11e6-8cdd-fbf217223d45.png)

![screen shot 2016-05-05 at 12 25 35 pm](https://cloud.githubusercontent.com/assets/346214/15042570/071ae992-12bd-11e6-9cf6-5aaba5e7fa17.png)
Closes https://github.com/facebook/react-native/pull/7406

Differential Revision: D3264567

Pulled By: mkonicek

fb-gh-sync-id: cfb73eaed56a7b5c6c84ce313e113393d152e9a1
fbshipit-source-id: cfb73eaed56a7b5c6c84ce313e113393d152e9a1

Examples/UIExplorer/PickerExample.js

@@ -0,0 +1,139 @@
+/**
+ * The examples provided by Facebook are for non-commercial testing and
+ * evaluation purposes only.
+ *
+ * Facebook reserves all rights not expressly granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON INFRINGEMENT. IN NO EVENT SHALL
+ * FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * @flow
+ */
+'use strict';
+
+const React = require('react');
+const ReactNative = require('react-native');
+const StyleSheet = require('StyleSheet');
+const UIExplorerBlock = require('UIExplorerBlock');
+const UIExplorerPage = require('UIExplorerPage');
+
+const {
+  Picker,
+  Text,
+  TouchableWithoutFeedback,
+} = ReactNative;
+const Item = Picker.Item;
+
+const PickerExample = React.createClass({
+
+  statics: {
+    title: '<Picker>',
+    description: 'Provides multiple options to choose from, using either a dropdown menu or a dialog.',
+  },
+
+  getInitialState: function() {
+    return {
+      selected1: 'key1',
+      selected2: 'key1',
+      selected3: 'key1',
+      color: 'red',
+      mode: Picker.MODE_DIALOG,
+    };
+  },
+
+  render: function() {
+    return (
+      <UIExplorerPage title="<Picker>">
+        <UIExplorerBlock title="Basic Picker">
+          <Picker
+            style={styles.picker}
+            selectedValue={this.state.selected1}
+            onValueChange={this.onValueChange.bind(this, 'selected1')}>
+            <Item label="hello" value="key0" />
+            <Item label="world" value="key1" />
+          </Picker>
+        </UIExplorerBlock>
+        <UIExplorerBlock title="Disabled picker">
+          <Picker style={styles.picker} enabled={false} selectedValue={this.state.selected1}>
+            <Item label="hello" value="key0" />
+            <Item label="world" value="key1" />
+          </Picker>
+        </UIExplorerBlock>
+        <UIExplorerBlock title="Dropdown Picker">
+          <Picker
+            style={styles.picker}
+            selectedValue={this.state.selected2}
+            onValueChange={this.onValueChange.bind(this, 'selected2')}
+            mode="dropdown">
+            <Item label="hello" value="key0" />
+            <Item label="world" value="key1" />
+          </Picker>
+        </UIExplorerBlock>
+        <UIExplorerBlock title="Picker with prompt message">
+          <Picker
+            style={styles.picker}
+            selectedValue={this.state.selected3}
+            onValueChange={this.onValueChange.bind(this, 'selected3')}
+            prompt="Pick one, just one">
+            <Item label="hello" value="key0" />
+            <Item label="world" value="key1" />
+          </Picker>
+        </UIExplorerBlock>
+        <UIExplorerBlock title="Picker with no listener">
+          <Picker style={styles.picker}>
+            <Item label="hello" value="key0" />
+            <Item label="world" value="key1" />
+          </Picker>
+          <Text>
+            Cannot change the value of this picker because it doesn't update selectedValue.
+          </Text>
+        </UIExplorerBlock>
+        <UIExplorerBlock title="Colorful pickers">
+          <Picker
+            style={[styles.picker, {color: 'white', backgroundColor: '#333'}]}
+            selectedValue={this.state.color}
+            onValueChange={this.onValueChange.bind(this, 'color')}
+            mode="dropdown">
+            <Item label="red" color="red" value="red" />
+            <Item label="green" color="green" value="green" />
+            <Item label="blue" color="blue" value="blue" />
+          </Picker>
+          <Picker
+            style={styles.picker}
+            selectedValue={this.state.color}
+            onValueChange={this.onValueChange.bind(this, 'color')}
+            mode="dialog">
+            <Item label="red" color="red" value="red" />
+            <Item label="green" color="green" value="green" />
+            <Item label="blue" color="blue" value="blue" />
+          </Picker>
+        </UIExplorerBlock>
+      </UIExplorerPage>
+    );
+  },
+
+  changeMode: function() {
+    const newMode = this.state.mode === Picker.MODE_DIALOG
+        ? Picker.MODE_DROPDOWN
+        : Picker.MODE_DIALOG;
+    this.setState({mode: newMode});
+  },
+
+  onValueChange: function(key: string, value: string) {
+    const newState = {};
+    newState[key] = value;
+    this.setState(newState);
+  },
+});
+
+var styles = StyleSheet.create({
+  picker: {
+    width: 100,
+  },
+});
+
+module.exports = PickerExample;