[Invalidations] Mark some member fields constants in FCM class

Change-Id: I63c4f71016101a761e6ecb67233bce79bf922fa3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1741920
Commit-Queue: Mohamed Amir Yosef <mamir@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689092}

components/invalidation/impl/fcm_invalidation_service.h

@@ -132,13 +132,13 @@ class FCMInvalidationService
   InvalidationLogger logger_;
 
   FCMNetworkHandlerCallback fcm_network_handler_callback_;
-  instance_id::InstanceIDDriver* instance_id_driver_;
+  instance_id::InstanceIDDriver* const instance_id_driver_;
   std::string client_id_;
 
-  IdentityProvider* identity_provider_;
-  PrefService* pref_service_;
-  syncer::ParseJSONCallback parse_json_;
-  network::mojom::URLLoaderFactory* loader_factory_;
+  IdentityProvider* const identity_provider_;
+  PrefService* const pref_service_;
+  syncer::ParseJSONCallback const parse_json_;
+  network::mojom::URLLoaderFactory* const loader_factory_;
   bool update_was_requested_ = false;
   Diagnostics diagnostic_info_;
 

components/invalidation/impl/per_user_topic_registration_manager.h

@@ -139,8 +139,8 @@ class INVALIDATION_EXPORT PerUserTopicRegistrationManager {
   net::BackoffEntry request_access_token_backoff_;
 
   // The callback for Parsing JSON.
-  ParseJSONCallback parse_json_;
-  network::mojom::URLLoaderFactory* url_loader_factory_;
+  ParseJSONCallback const parse_json_;
+  network::mojom::URLLoaderFactory* const url_loader_factory_;
 
   const std::string project_id_;
   const bool migrate_prefs_;