Log JSBundleRequireTime and JSAppRequireTime.

Reviewed By: javache

Differential Revision: D2590707

fb-gh-sync-id: 4c306342b5725aaaac1d8fa0257ef860e446b0d4

Libraries/Utilities/PerformanceLogger.js

@@ -71,11 +71,21 @@ var PerformanceLogger = {
       timespans[key].endTime - timespans[key].startTime;
   },
 
-  clearTimespans() {
+  clear() {
     timespans = {};
     extras = {};
   },
 
+  clearExceptTimespans(keys) {
+    timespans = Object.keys(timespans).reduce(function(previous, key) {
+      if (keys.indexOf(key) !== -1) {
+        previous[key] = timespans[key];
+      }
+      return previous;
+    }, {});
+    extras = {};
+  },
+
   getTimespans() {
     return timespans;
   },