[SyncFS] Add ScopedEnableSyncFSV2 for testing

chrome/browser/sync_file_system/syncable_file_system_util.h

Index: chrome/browser/sync_file_system/syncable_file_system_util.h
diff --git a/chrome/browser/sync_file_system/syncable_file_system_util.h b/chrome/browser/sync_file_system/syncable_file_system_util.h
index 7e28607f8f8c3ee85f9581b7b8c1575539d1cede..35512ca4f073dcb75281abd230b6e005360dfb40 100644
--- a/chrome/browser/sync_file_system/syncable_file_system_util.h
+++ b/chrome/browser/sync_file_system/syncable_file_system_util.h
@@ -115,6 +115,18 @@ class ScopedEnableSyncFSDirectoryOperation {
   DISALLOW_COPY_AND_ASSIGN(ScopedEnableSyncFSDirectoryOperation);
 };
 
+// Enables V2 backend for syncable filesystems temporarily for testing.
+class ScopedEnableSyncFSV2 {
+ public:
+  ScopedEnableSyncFSV2();
+  ~ScopedEnableSyncFSV2();
+
+ private:
+  bool was_enabled_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedEnableSyncFSV2);
+};
+
 // Posts |callback| to the current thread.
 void RunSoon(const tracked_objects::Location& from_here,
              const base::Closure& callback);