Add Performance and Firestore strings to FIRApp (#394)

Author: paulb777

Firebase/Core/FIRApp.m

@@ -27,10 +27,12 @@
 NSString *const kFIRServiceCrash = @"Crash";
 NSString *const kFIRServiceDatabase = @"Database";
 NSString *const kFIRServiceDynamicLinks = @"DynamicLinks";
+NSString *const kFIRServiceFirestore = @"Firestore";
 NSString *const kFIRServiceInstanceID = @"InstanceID";
 NSString *const kFIRServiceInvites = @"Invites";
 NSString *const kFIRServiceMessaging = @"Messaging";
 NSString *const kFIRServiceMeasurement = @"Measurement";
+NSString *const kFIRServicePerformance = @"Performance";
 NSString *const kFIRServiceRemoteConfig = @"RemoteConfig";
 NSString *const kFIRServiceStorage = @"Storage";
 NSString *const kGGLServiceAnalytics = @"Analytics";