sync: Fix serialization in proto_value_conversions

Adds proper serialiation for the 'initial_sync_in_progress' flag.

This should have been part of r284159.

BUG=351005

Review URL: https://codereview.chromium.org/453143002

Cr-Commit-Position: refs/heads/master@{#288494}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288494 0039d316-1c4b-4281-b951-d872f2087c98

sync/protocol/proto_value_conversions.cc

@@ -897,6 +897,7 @@ base::DictionaryValue* GetUpdateTriggersToValue(
   SET_BOOL(invalidations_out_of_sync);
   SET_INT64(local_modification_nudges);
   SET_INT64(datatype_refresh_nudges);
+  SET_BOOL(initial_sync_in_progress);
   return value;
 }