Add new onInput event

'input' is supported in IE9+ and all other browsers according to
https://developer.mozilla.org/en-US/docs/Web/API/window.oninput

Test Plan:
Modified ballmer-peak example to use onInput instead of onKeyUp and
tested that it works properly on latest Chrome.

src/core/ReactEvent.js

@@ -211,6 +211,7 @@ function listenAtTopLevel(touchNotMouse) {
   trapBubbledEvent(topLevelTypes.topKeyUp, 'keyup', mountAt);
   trapBubbledEvent(topLevelTypes.topKeyPress, 'keypress', mountAt);
   trapBubbledEvent(topLevelTypes.topKeyDown, 'keydown', mountAt);
+  trapBubbledEvent(topLevelTypes.topInput, 'input', mountAt);
   trapBubbledEvent(topLevelTypes.topChange, 'change', mountAt);
   trapBubbledEvent(
     topLevelTypes.topDOMCharacterDataModified,

src/event/EventConstants.js

@@ -32,6 +32,7 @@ var topLevelTypes = keyMirror({
   topDOMCharacterDataModified: null,
   topDoubleClick: null,
   topFocus: null,
+  topInput: null,
   topKeyDown: null,
   topKeyPress: null,
   topKeyUp: null,

src/eventPlugins/SimpleEventPlugin.js

@@ -108,6 +108,12 @@ var SimpleEventPlugin = {
         captured: keyOf({onKeyDownCapture: true})
       }
     },
+    input: {
+      phasedRegistrationNames: {
+        bubbled: keyOf({onInput: true}),
+        captured: keyOf({onInputCapture: true})
+      }
+    },
     focus: {
       phasedRegistrationNames: {
         bubbled: keyOf({onFocus: true}),
@@ -220,6 +226,7 @@ SimpleEventPlugin.topLevelTypesToAbstract = {
   topKeyUp:       SimpleEventPlugin.abstractEventTypes.keyUp,
   topKeyPress:    SimpleEventPlugin.abstractEventTypes.keyPress,
   topKeyDown:     SimpleEventPlugin.abstractEventTypes.keyDown,
+  topInput:       SimpleEventPlugin.abstractEventTypes.input,
   topFocus:       SimpleEventPlugin.abstractEventTypes.focus,
   topBlur:        SimpleEventPlugin.abstractEventTypes.blur,
   topScroll:      SimpleEventPlugin.abstractEventTypes.scroll,