Simulate transient error and verify exponential backoff.

chrome/browser/sync/sessions/session_state.h

Index: chrome/browser/sync/sessions/session_state.h
diff --git a/chrome/browser/sync/sessions/session_state.h b/chrome/browser/sync/sessions/session_state.h
index 85d683b69f4192ff7cd8c4476bdca72104c6d9b5..490f7c0611aef990a1a01a163dbf52e5a0538122 100644
--- a/chrome/browser/sync/sessions/session_state.h
+++ b/chrome/browser/sync/sessions/session_state.h
@@ -130,7 +130,8 @@ struct SyncSessionSnapshot {
       int num_conflicting_updates,
       bool did_commit_items,
       const SyncSourceInfo& source,
-      size_t num_entries);
+      size_t num_entries,
+      base::Time sync_start_time);
   ~SyncSessionSnapshot();
 
   // Caller takes ownership of the returned dictionary.
@@ -152,6 +153,7 @@ struct SyncSessionSnapshot {
   const bool did_commit_items;
   const SyncSourceInfo source;
   const size_t num_entries;
+  base::Time sync_start_time;
 };
 
 // Tracks progress of conflicts and their resolution using conflict sets.