[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 3fb2c5bed8f7aa27c2b0c183884d715af6033440..2542cd1a8ca31e4d5c64d26c191b4cb05e8a6479 100644
--- a/components/browser_sync/profile_sync_service.h
+++ b/components/browser_sync/profile_sync_service.h
@@ -246,6 +246,7 @@ class ProfileSyncService : public syncer::SyncService,
     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);
@@ -263,6 +264,7 @@ class ProfileSyncService : public syncer::SyncService,
   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;
@@ -838,6 +840,9 @@ class ProfileSyncService : public syncer::SyncService,
   // 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_;
+
   // Encapsulates user signin - used to set/get the user's authenticated
   // email address.
   const std::unique_ptr<SigninManagerWrapper> signin_;