[Sync] Replace manual DI with SetTestingFactory.

components/sync/driver/fake_sync_service.h

Index: components/sync/driver/fake_sync_service.h
diff --git a/components/sync/driver/fake_sync_service.h b/components/sync/driver/fake_sync_service.h
index 086953eec4289299f5847f5953d58b17d4832edf..095fbc1cba37db5264212ba5edf6c6f60402e09d 100644
--- a/components/sync/driver/fake_sync_service.h
+++ b/components/sync/driver/fake_sync_service.h
@@ -24,7 +24,7 @@ class FakeSyncService : public SyncService {
   ~FakeSyncService() override;
 
  private:
-  // SyncService:
+  // SyncService implementation.
   bool IsFirstSetupComplete() const override;
   bool IsSyncAllowed() const override;
   bool IsSyncActive() const override;
@@ -85,10 +85,13 @@ class FakeSyncService : public SyncService {
                        callback) override;
   SigninManagerBase* signin() const override;
 
-  // DataTypeEncryptionHandler:
+  // DataTypeEncryptionHandler implementation.
   bool IsPassphraseRequired() const override;
   ModelTypeSet GetEncryptedDataTypes() const override;
 
+  // KeyedService implementation.
+  void Shutdown() override;
+
   GoogleServiceAuthError error_;
   GURL sync_service_url_;
   std::string unrecoverable_error_message_;