Sync FileSystem: Add simulated relaunch of DriveFileSyncService on its unit_tests

chrome/browser/sync_file_system/drive_file_sync_service.h

Index: chrome/browser/sync_file_system/drive_file_sync_service.h
diff --git a/chrome/browser/sync_file_system/drive_file_sync_service.h b/chrome/browser/sync_file_system/drive_file_sync_service.h
index 3232e5f1bf52a5b595cbbdc90e0059b00238a07a..0a6c457e3ac596737a6fc364c2fc7137c3d54834 100644
--- a/chrome/browser/sync_file_system/drive_file_sync_service.h
+++ b/chrome/browser/sync_file_system/drive_file_sync_service.h
@@ -62,6 +62,12 @@ class DriveFileSyncService
       scoped_ptr<DriveFileSyncClientInterface> sync_client,
       scoped_ptr<DriveMetadataStore> metadata_store);
 
+  // Destroy |sync_service| and pass the ownership of |sync_client| to caller
+  // for testing.
+  static scoped_ptr<DriveFileSyncClientInterface>
+  DestroyAndPassSyncClientForTesting(
+      scoped_ptr<DriveFileSyncService> sync_service);
+
   // RemoteFileSyncService overrides.
   virtual void AddServiceObserver(Observer* observer) OVERRIDE;
   virtual void AddFileStatusObserver(FileStatusObserver* observer) OVERRIDE;