Add onLoadX support on Android

Summary: ~~This is a WIP, just finished the first bit and wanted to get some feedback to see if this approach seems appropriate, as I haven't done a lot of Android development.~~

Looks ready for review now.
Closes https://github.com/facebook/react-native/pull/3791

Reviewed By: svcscm

Differential Revision: D2672262

Pulled By: mkonicek

fb-gh-sync-id: 1e8f1cc6658fb719a68f7da455f30a7c9b1db730

Examples/UIExplorer/ImageExample.js

@@ -28,6 +28,44 @@ var base64Icon = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAEsAAABLCAQAAACS
 
 var ImageCapInsetsExample = require('./ImageCapInsetsExample');
 
+var NetworkImageCallbackExample = React.createClass({
+  getInitialState: function() {
+    return {
+      events: [],
+    };
+  },
+
+  componentWillMount() {
+    this.setState({mountTime: new Date()});
+  },
+
+  render: function() {
+    var { mountTime } = this.state;
+
+    return (
+      <View>
+        <Image
+          source={this.props.source}
+          style={[styles.base, {overflow: 'visible'}]}
+          onLoadStart={() => this._loadEventFired(`✔ onLoadStart (+${new Date() - mountTime}ms)`)}
+          onLoad={() => this._loadEventFired(`✔ onLoad (+${new Date() - mountTime}ms)`)}
+          onLoadEnd={() => this._loadEventFired(`✔ onLoadEnd (+${new Date() - mountTime}ms)`)}
+        />
+
+        <Text style={{marginTop: 20}}>
+          {this.state.events.join('\n')}
+        </Text>
+      </View>
+    );
+  },
+
+  _loadEventFired(event) {
+    this.setState((state) => {
+      return state.events = [...state.events, event];
+    });
+  }
+});
+
 var NetworkImageExample = React.createClass({
   watchID: (null: ?number),
 
@@ -92,6 +130,14 @@ exports.examples = [
       );
     },
   },
+  {
+    title: 'Image Loading Events',
+    render: function() {
+      return (
+        <NetworkImageCallbackExample source={{uri: 'http://facebook.github.io/origami/public/images/blog-hero.jpg?r=1'}}/>
+      );
+    },
+  },
   {
     title: 'Error Handler',
     render: function() {