[Sync] Convert SyncSessionSnapshot to a copy-able class.

sync/internal_api/js_sync_manager_observer.cc

Index: sync/internal_api/js_sync_manager_observer.cc
diff --git a/sync/internal_api/js_sync_manager_observer.cc b/sync/internal_api/js_sync_manager_observer.cc
index b9cf9f320c644185c3da152fd2b1048d0261bfa1..5aa9dc34ca9632563c6070d89ad68eb49e302cbe 100644
--- a/sync/internal_api/js_sync_manager_observer.cc
+++ b/sync/internal_api/js_sync_manager_observer.cc
@@ -31,12 +31,12 @@ void JsSyncManagerObserver::SetJsEventHandler(
 }
 
 void JsSyncManagerObserver::OnSyncCycleCompleted(
-    const sessions::SyncSessionSnapshot* snapshot) {
+    const sessions::SyncSessionSnapshot& snapshot) {
   if (!event_handler_.IsInitialized()) {
     return;
   }
   DictionaryValue details;
-  details.Set("snapshot", snapshot->ToValue());
+  details.Set("snapshot", snapshot.ToValue());
   HandleJsEvent(FROM_HERE, "onSyncCycleCompleted", JsEventDetails(&details));
 }