Sync: Support multiple setup UIs.

components/browser_sync/browser/profile_sync_service.h

Index: components/browser_sync/browser/profile_sync_service.h
diff --git a/components/browser_sync/browser/profile_sync_service.h b/components/browser_sync/browser/profile_sync_service.h
index 3fecc3197fa8b306fb396ec8b051385d7a41aae3..21570498856c9d50b3f80d3146dde40dcaa387c1 100644
--- a/components/browser_sync/browser/profile_sync_service.h
+++ b/components/browser_sync/browser/profile_sync_service.h
@@ -165,14 +165,16 @@ class EncryptedData;
 //   that control the initial sync download:
 //
 //    * SetFirstSetupComplete()
-//    * SetSetupInProgress()
+//    * GetSetupInProgressHandle()
 //
 //   SetFirstSetupComplete() should be called once the user has finished setting
-//   up sync at least once on their account. SetSetupInProgress(true) should be
-//   called while the user is actively configuring their account, and then
-//   SetSetupInProgress(false) should be called when configuration is complete.
-//   Once both these conditions have been met, CanConfigureDataTypes() will
-//   return true and datatype configuration can begin.
+//   up sync at least once on their account. GetSetupInProgressHandle() should
+//   be called while the user is actively configuring their account. The handle
+//   should be deleted once configuration is complete.
+//
+//   Once first setup has completed and there are no outstanding
+//   setup-in-progress handles, CanConfigureDataTypes() will return true and
+//   datatype configuration can begin.
 class ProfileSyncService : public sync_driver::SyncService,
                            public sync_driver::SyncFrontend,
                            public sync_driver::SyncPrefObserver,
@@ -280,7 +282,8 @@ class ProfileSyncService : public sync_driver::SyncService,
                             syncer::ModelTypeSet chosen_types) override;
   void SetFirstSetupComplete() override;
   bool IsFirstSetupInProgress() const override;
-  void SetSetupInProgress(bool setup_in_progress) override;
+  std::unique_ptr<sync_driver::SyncSetupInProgressHandle>
+  GetSetupInProgressHandle() override;
   bool IsSetupInProgress() const override;
   bool ConfigurationDone() const override;
   const GoogleServiceAuthError& GetAuthError() const override;
@@ -802,6 +805,9 @@ class ProfileSyncService : public sync_driver::SyncService,
   // True if setup has been completed at least once and is not in progress.
   bool CanConfigureDataTypes() const;
 
+  // Called when a SetupInProgressHandle issued by this instance is destroyed.
+  virtual void OnSetupInProgressHandleDestroyed();
+
   // This profile's SyncClient, which abstracts away non-Sync dependencies and
   // the Sync API component factory.
   std::unique_ptr<sync_driver::SyncClient> sync_client_;
@@ -844,6 +850,10 @@ class ProfileSyncService : public sync_driver::SyncService,
   // is equal to !IsFirstSetupComplete() at the time of OnBackendInitialized().
   bool is_first_time_sync_configure_;
 
+  // Number of UIs currently configuring the Sync service. When this number
+  // is decremented back to zero, Sync setup is marked no longer in progress.
+  int outstanding_setup_in_progress_handles_ = 0;
+
   // List of available data type controllers.
   sync_driver::DataTypeController::TypeMap data_type_controllers_;