Fix unmounting performance regression in V8 (#7232)

As reported in #7227, unmounting performance regressed with React 15.
It seems that `delete` has become much slower since we started using numeric keys.
Forcing dictionary keys to start with a dot fixes the issue.
(cherry picked from commit 64e7602b3b)

src/renderers/dom/client/eventPlugins/SimpleEventPlugin.js

@@ -483,6 +483,10 @@ for (var type in topLevelEventsToDispatchConfig) {
 var ON_CLICK_KEY = keyOf({onClick: null});
 var onClickListeners = {};
 
+function getDictionaryKey(inst) {
+  return '.' + inst._rootNodeID;
+}
+
 var SimpleEventPlugin = {
 
   eventTypes: eventTypes,
@@ -620,10 +624,10 @@ var SimpleEventPlugin = {
     // fire. The workaround for this bug involves attaching an empty click
     // listener on the target node.
     if (registrationName === ON_CLICK_KEY) {
-      var id = inst._rootNodeID;
+      var key = getDictionaryKey(inst);
       var node = ReactDOMComponentTree.getNodeFromInstance(inst);
-      if (!onClickListeners[id]) {
-        onClickListeners[id] = EventListener.listen(
+      if (!onClickListeners[key]) {
+        onClickListeners[key] = EventListener.listen(
           node,
           'click',
           emptyFunction
@@ -634,9 +638,9 @@ var SimpleEventPlugin = {
 
   willDeleteListener: function(inst, registrationName) {
     if (registrationName === ON_CLICK_KEY) {
-      var id = inst._rootNodeID;
-      onClickListeners[id].remove();
-      delete onClickListeners[id];
+      var key = getDictionaryKey(inst);
+      onClickListeners[key].remove();
+      delete onClickListeners[key];
     }
   },
 

src/renderers/shared/stack/event/EventPluginHub.js

@@ -53,6 +53,10 @@ var executeDispatchesAndReleaseTopLevel = function(e) {
   return executeDispatchesAndRelease(e, false);
 };
 
+var getDictionaryKey = function(inst) {
+  return '.' + inst._rootNodeID;
+};
+
 /**
  * This is a unified interface for event plugins to be installed and configured.
  *
@@ -96,7 +100,7 @@ var EventPluginHub = {
   },
 
   /**
-   * Stores `listener` at `listenerBank[registrationName][id]`. Is idempotent.
+   * Stores `listener` at `listenerBank[registrationName][key]`. Is idempotent.
    *
    * @param {object} inst The instance, which is the source of events.
    * @param {string} registrationName Name of listener (e.g. `onClick`).
@@ -109,9 +113,10 @@ var EventPluginHub = {
       registrationName, typeof listener
     );
 
+    var key = getDictionaryKey(inst);
     var bankForRegistrationName =
       listenerBank[registrationName] || (listenerBank[registrationName] = {});
-    bankForRegistrationName[inst._rootNodeID] = listener;
+    bankForRegistrationName[key] = listener;
 
     var PluginModule =
       EventPluginRegistry.registrationNameModules[registrationName];
@@ -127,7 +132,8 @@ var EventPluginHub = {
    */
   getListener: function(inst, registrationName) {
     var bankForRegistrationName = listenerBank[registrationName];
-    return bankForRegistrationName && bankForRegistrationName[inst._rootNodeID];
+    var key = getDictionaryKey(inst);
+    return bankForRegistrationName && bankForRegistrationName[key];
   },
 
   /**
@@ -146,7 +152,8 @@ var EventPluginHub = {
     var bankForRegistrationName = listenerBank[registrationName];
     // TODO: This should never be null -- when is it?
     if (bankForRegistrationName) {
-      delete bankForRegistrationName[inst._rootNodeID];
+      var key = getDictionaryKey(inst);
+      delete bankForRegistrationName[key];
     }
   },
 
@@ -156,12 +163,13 @@ var EventPluginHub = {
    * @param {object} inst The instance, which is the source of events.
    */
   deleteAllListeners: function(inst) {
+    var key = getDictionaryKey(inst);
     for (var registrationName in listenerBank) {
       if (!listenerBank.hasOwnProperty(registrationName)) {
         continue;
       }
-      
-      if (!listenerBank[registrationName][inst._rootNodeID]) {
+
+      if (!listenerBank[registrationName][key]) {
         continue;
       }
 
@@ -171,7 +179,7 @@ var EventPluginHub = {
         PluginModule.willDeleteListener(inst, registrationName);
       }
 
-      delete listenerBank[registrationName][inst._rootNodeID];
+      delete listenerBank[registrationName][key];
     }
   },