Add missing class annotations xplat/js

Reviewed By: SamChou19815

Differential Revision: D38373443

fbshipit-source-id: 1222c4845ebd6b72bd6f54af1a27cf8542dd883a

Libraries/Utilities/createPerformanceLogger.js

@@ -137,31 +137,31 @@ class PerformanceLogger implements IPerformanceLogger {
     this._closed = true;
   }
 
-  currentTimestamp() {
+  currentTimestamp(): number {
     return getCurrentTimestamp();
   }
 
-  getExtras() {
+  getExtras(): {[key: string]: ?ExtraValue} {
     return this._extras;
   }
 
-  getPoints() {
+  getPoints(): {[key: string]: ?number} {
     return this._points;
   }
 
-  getPointExtras() {
+  getPointExtras(): {[key: string]: ?Extras} {
     return this._pointExtras;
   }
 
-  getTimespans() {
+  getTimespans(): {[key: string]: ?Timespan} {
     return this._timespans;
   }
 
-  hasTimespan(key: string) {
+  hasTimespan(key: string): boolean {
     return !!this._timespans[key];
   }
 
-  isClosed() {
+  isClosed(): boolean {
     return this._closed;
   }