Introduce the plumbing necessary to report Unrecoverable error from model safe workers.

chrome/browser/sync/engine/update_applicator.cc

Index: chrome/browser/sync/engine/update_applicator.cc
diff --git a/chrome/browser/sync/engine/update_applicator.cc b/chrome/browser/sync/engine/update_applicator.cc
index 60f2c36aeb353c79365a4920d821a2b3aeebf849..fa32fc64c1cd69e902dc5b5e44bfac2b1e6e0011 100644
--- a/chrome/browser/sync/engine/update_applicator.cc
+++ b/chrome/browser/sync/engine/update_applicator.cc
@@ -79,6 +79,9 @@ bool UpdateApplicator::AttemptOneApplication(
       pointer_++;
       application_results_.AddEncryptionConflict(entry.Get(syncable::ID));
       break;
+    case FAILED_UPDATE:
+      application_results_.set_failed_update();
+      return false;
     default:
       NOTREACHED();
       break;
@@ -126,7 +129,12 @@ void UpdateApplicator::SaveProgressIntoSessionState(
   application_results_.SaveProgress(conflict_progress, update_progress);
 }
 
-UpdateApplicator::ResultTracker::ResultTracker(size_t num_results) {
+bool UpdateApplicator::failed_update() const {
+  return application_results_.failed_udpate();
+}
+
+UpdateApplicator::ResultTracker::ResultTracker(size_t num_results) :
+    failed_update_(false) {
   successful_ids_.reserve(num_results);
 }
 
@@ -145,6 +153,14 @@ void UpdateApplicator::ResultTracker::AddSuccess(syncable::Id id) {
   successful_ids_.push_back(id);
 }
 
+void UpdateApplicator::ResultTracker::set_failed_update() {
+  failed_update_ = true;
+}
+
+bool UpdateApplicator::ResultTracker::failed_udpate() const {
+  return failed_update_;
+}
+
 void UpdateApplicator::ResultTracker::SaveProgress(
     sessions::ConflictProgress* conflict_progress,
     sessions::UpdateProgress* update_progress) {