Add support for ontimeout and onerror handler when using XMLHttpRequest for Android and iOS

Summary:Currently React-Native does not have `ontimeout` and `onerror` handlers for [XMLHttpRequest](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest). This is an extension to [No timeout on XMLHttpRequest](https://github.com/facebook/react-native/issues/4648).

With addition to two handlers, both Android and iOS can now handle `ontimeout` if request times out and `onerror` when there is general network error.

**Test plan**

Code has been tested on both Android and iOS with [Charles](https://www.charlesproxy.com/) by setting a breakpoint on the request which fires `ontimeout` when the request waits beyond `timeout` time and `onerror` when there is network error.

**Usage**

JavaScript -

```
var request = new XMLHttpRequest();

function onLoad() {
    console.log(request.status);
};

function onTimeout() {
    console.log('Timeout');
};

function onError() {
    console.log('General network error');
};

request.onload = onLoad;
request.ontimeout = onTimeout;
request.onerr
Closes https://github.com/facebook/react-native/pull/6841

Differential Revision: D3178859

Pulled By: lexs

fb-gh-sync-id: 30674570653e92ab5f7e74bd925dd5640fc862b6
fbshipit-source-id: 30674570653e92ab5f7e74bd925dd5640fc862b6

Examples/UIExplorer/XHRExampleOnTimeOut.js

@@ -0,0 +1,110 @@
+/**
+ * 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';
+
+var React = require('react');
+var ReactNative = require('react-native');
+var {
+  StyleSheet,
+  Text,
+  TouchableHighlight,
+  View,
+} = ReactNative;
+
+class XHRExampleOnTimeOut extends React.Component {
+  state: any;
+  xhr: XMLHttpRequest;
+
+  constructor(props: any) {
+    super(props);
+    this.state = {
+      status: '',
+      loading: false
+    };
+  }
+
+  loadTimeOutRequest() {
+    this.xhr && this.xhr.abort();
+
+    var xhr = this.xhr || new XMLHttpRequest();
+
+    xhr.onerror = ()=> {
+      console.log('Status ', xhr.status);
+      console.log('Error ', xhr.responseText);
+    };
+
+    xhr.ontimeout = () => {
+      this.setState({
+        status: xhr.responseText,
+        loading: false
+      });
+    };
+
+    xhr.onload = () => {
+      console.log('Status ', xhr.status);
+      console.log('Response ', xhr.responseText);
+    };
+
+    xhr.open('GET', 'https://httpbin.org/delay/5'); // request to take 5 seconds to load
+    xhr.timeout = 2000; // request times out in 2 seconds
+    xhr.send();
+    this.xhr = xhr;
+
+    this.setState({loading: true});
+  }
+
+  componentWillUnmount() {
+    this.xhr && this.xhr.abort();
+  }
+
+  render() {
+    var button = this.state.loading ? (
+      <View style={styles.wrapper}>
+        <View style={styles.button}>
+          <Text>Loading...</Text>
+        </View>
+      </View>
+    ) : (
+      <TouchableHighlight
+        style={styles.wrapper}
+        onPress={this.loadTimeOutRequest.bind(this)}>
+        <View style={styles.button}>
+         <Text>Make Time Out Request</Text>
+        </View>
+      </TouchableHighlight>
+    );
+
+    return (
+      <View>
+        {button}
+        <Text>{this.state.status}</Text>
+      </View>
+    );
+  }
+}
+
+var styles = StyleSheet.create({
+  wrapper: {
+    borderRadius: 5,
+    marginBottom: 5,
+  },
+  button: {
+    backgroundColor: '#eeeeee',
+    padding: 8,
+  },
+});
+
+module.exports = XHRExampleOnTimeOut;