[Sync] Allow sync start without sign-in if the local sync backend is on.

components/browser_sync/profile_sync_service.h

Index: components/browser_sync/profile_sync_service.h
diff --git a/components/browser_sync/profile_sync_service.h b/components/browser_sync/profile_sync_service.h
index 92356b5147505c0b40d538deee023157c04051ef..8aaf07b51960b97230da5229b3fa02dcb1e5b166 100644
--- a/components/browser_sync/profile_sync_service.h
+++ b/components/browser_sync/profile_sync_service.h
@@ -245,6 +245,7 @@ class ProfileSyncService : public syncer::SyncServiceBase,
     std::string debug_identifier;
     version_info::Channel channel = version_info::Channel::UNKNOWN;
     base::SequencedWorkerPool* blocking_pool = nullptr;
+    base::FilePath local_sync_backend_folder;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(InitParams);
@@ -262,6 +263,7 @@ class ProfileSyncService : public syncer::SyncServiceBase,
   bool IsFirstSetupComplete() const override;
   bool IsSyncAllowed() const override;
   bool IsSyncActive() const override;
+  bool IsLocalSyncEnabled() const override;
   void TriggerRefresh(const syncer::ModelTypeSet& types) override;
   void OnDataTypeRequestsSyncStartup(syncer::ModelType type) override;
   bool CanSyncStart() const override;
@@ -814,6 +816,9 @@ class ProfileSyncService : public syncer::SyncServiceBase,
   // engine to refresh its credentials.
   bool is_auth_in_progress_;
 
+  // The location where the local sync backend stores its data.
+  base::FilePath local_sync_backend_folder_;
+
   // Information describing an unrecoverable error.
   UnrecoverableErrorReason unrecoverable_error_reason_;
   std::string unrecoverable_error_message_;