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

Libraries/Image/Image.android.js

@@ -56,6 +56,7 @@ var ImageViewAttributes = merge(ReactNativeViewAttributes.UIView, {
   resizeMode: true,
   progressiveRenderingEnabled: true,
   fadeDuration: true,
+  shouldNotifyLoadEvents: true,
 });
 
 var Image = React.createClass({
@@ -75,7 +76,18 @@ var Image = React.createClass({
     ]).isRequired,
     progressiveRenderingEnabled: PropTypes.bool,
     fadeDuration: PropTypes.number,
-    style: StyleSheetPropType(ImageStylePropTypes),
+    /**
+     * Invoked on load start
+     */
+    onLoadStart: PropTypes.func,
+    /**
+     * Invoked when load completes successfully
+     */
+    onLoad: PropTypes.func,
+    /**
+     * Invoked when load either succeeds or fails
+     */
+    onLoadEnd: PropTypes.func,
     /**
      * Used to locate this view in end-to-end tests.
      */
@@ -137,9 +149,11 @@ var Image = React.createClass({
     if (source && source.uri) {
       var {width, height} = source;
       var style = flattenStyle([{width, height}, styles.base, this.props.style]);
+      var {onLoadStart, onLoad, onLoadEnd} = this.props;
 
       var nativeProps = merge(this.props, {
         style,
+        shouldNotifyLoadEvents: !!(onLoadStart || onLoad || onLoadEnd),
         src: source.uri,
       });
 
@@ -186,6 +200,7 @@ var cfg = {
     defaultImageSrc: true,
     imageTag: true,
     progressHandlerRegistered: true,
+    shouldNotifyLoadEvents: true,
   },
 };
 var RKImage = requireNativeComponent('RCTImageView', Image, cfg);

Libraries/Image/Image.ios.js

@@ -113,7 +113,6 @@ var Image = React.createClass({
     onLayout: PropTypes.func,
     /**
      * Invoked on load start
-     * @platform ios
      */
     onLoadStart: PropTypes.func,
     /**
@@ -128,12 +127,10 @@ var Image = React.createClass({
     onError: PropTypes.func,
     /**
      * Invoked when load completes successfully
-     * @platform ios
      */
     onLoad: PropTypes.func,
     /**
      * Invoked when load either succeeds or fails
-     * @platform ios
      */
     onLoadEnd: PropTypes.func,
   },