Fix all warnings for missing keys.

Summary:
I had to go through each component while debugging for another issue and decided to clean these warnings up along the way.
Closes https://github.com/facebook/react-native/pull/4653

Reviewed By: svcscm

Differential Revision: D2752740

Pulled By: androidtrunkagent

fb-gh-sync-id: 94da8ad693cae04e353f33f540c15214f6f3e7d8

Examples/UIExplorer/TimerExample.js

@@ -171,9 +171,20 @@ exports.examples = [
           }
           return (
             <View>
-              {timer}
+              {this.state.showTimer && this._renderTimer()}
               <UIExplorerButton onPress={this._toggleTimer}>
-                {toggleText}
+                {this.state.showTimer ? 'Unmount timer' : 'Mount new timer'}
+              </UIExplorerButton>
+            </View>
+          );
+        },
+
+        _renderTimer: function() {
+          return (
+            <View>
+              <TimerTester ref="interval" dt={25} type="setInterval" />
+              <UIExplorerButton onPress={() => this.refs.interval.clear() }>
+                Clear interval
               </UIExplorerButton>
             </View>
           );