[Sync] Don't start up sync when FirstSetupCompleted is false and no setup in progress

components/sync_driver/startup_controller.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_SYNC_DRIVER_STARTUP_CONTROLLER_H_
 #define COMPONENTS_SYNC_DRIVER_STARTUP_CONTROLLER_H_
 
 #include "base/callback.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
@@ skipping 11 matching lines @@
 class StartupController {
  public:
   StartupController(const sync_driver::SyncPrefs* sync_prefs,
                     base::Callback<bool()> can_start,
                     base::Closure start_backend);
   ~StartupController();
 
   // Starts up sync if it is requested by the user and preconditions are met.
   // Returns true if these preconditions are met, although does not imply
   // the backend was started.
-  bool TryStart();
+  // |request_immediate| will force immediate startup if true, rather than
+  // deferred, once preconditions are met.
+  bool TryStart(bool request_immediate);

[maxbogue, 2016/07/15 21:44:48]

I think the code will be much more readable if you add a second method like
TryStartImmediately() instead of a boolean parameter. It would just set
received_start_request_ and then call TryStart().

[Nicolas Zea, 2016/07/15 22:42:22]

Good call, done.

 
   // Called when a datatype (SyncableService) has a need for sync to start
   // ASAP, presumably because a local change event has occurred but we're
   // still in deferred start mode, meaning the SyncableService hasn't been
   // told to MergeDataAndStartSyncing yet.
   // It is expected that |type| is a currently active datatype.
   void OnDataTypeRequestsSyncStartup(syncer::ModelType type);
 
   // Prepares this object for a new attempt to start sync, forgetting
   // whether or not preconditions were previously met.
@@ skipping 57 matching lines @@
 
   // Used to compute preferred_types from SyncPrefs as-needed.
   syncer::ModelTypeSet registered_types_;
 
   base::WeakPtrFactory<StartupController> weak_factory_;
 };
 
 }  // namespace browser_sync
 
 #endif  // COMPONENTS_SYNC_DRIVER_STARTUP_CONTROLLER_H_