Fix transition end detection for Android

Some Android versions have the "transition" and "animation" properties
set on element style objects despite not supporting un-prefxied animations
and transitions.  This change adds an additional sanity check to make sure
the correct event handlers are added for transition groups.

src/addons/transitions/ReactTransitionEvents.js

@@ -20,6 +20,11 @@
 
 var ExecutionEnvironment = require('ExecutionEnvironment');
 
+/**
+ * EVENT_NAME_MAP is used to determine which event fired when a
+ * transition/animation ends, based on the style property used to
+ * define that event.
+ */
 var EVENT_NAME_MAP = {
   transitionend: {
     'transition': 'transitionend',
@@ -43,6 +48,20 @@ var endEvents = [];
 function detectEvents() {
   var testEl = document.createElement('div');
   var style = testEl.style;
+
+  // On some platforms, in particular some releases of Android 4.x,
+  // the un-prefixed "animation" and "transition" properties are defined on the
+  // style object but the events that fire will still be prefixed, so we need
+  // to check if the un-prefixed events are useable, and if not remove them
+  // from the map
+  if (!('AnimationEvent' in window)) {
+    delete EVENT_NAME_MAP.animationend.animation;
+  }
+
+  if (!('TransitionEvent' in window)) {
+   delete EVENT_NAME_MAP.transitionend.transition;
+  }
+
   for (var baseEventName in EVENT_NAME_MAP) {
     var baseEvents = EVENT_NAME_MAP[baseEventName];
     for (var styleName in baseEvents) {