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

chrome/browser/sync/engine/update_applicator.h

Index: chrome/browser/sync/engine/update_applicator.h
diff --git a/chrome/browser/sync/engine/update_applicator.h b/chrome/browser/sync/engine/update_applicator.h
index 1196fccf29f5128678c2ecbd8415c46d630c1783..96529bc70dba083117d209faad4a56d99c4b58fc 100644
--- a/chrome/browser/sync/engine/update_applicator.h
+++ b/chrome/browser/sync/engine/update_applicator.h
@@ -55,6 +55,8 @@ class UpdateApplicator {
       sessions::ConflictProgress* conflict_progress,
       sessions::UpdateProgress* update_progress);
 
+  bool failed_update() const;
+
  private:
   // Track the status of all applications.
   // We treat encryption conflicts as nonblocking conflict items when we save
@@ -69,6 +71,8 @@ class UpdateApplicator {
      void SaveProgress(sessions::ConflictProgress* conflict_progress,
                        sessions::UpdateProgress* update_progress);
      void ClearConflicts();
+     void set_failed_update();
+     bool failed_udpate() const;
 
      // Returns true iff conflicting_ids_ is empty. Does not check
      // encryption_conflict_ids_.
@@ -77,6 +81,7 @@ class UpdateApplicator {
     std::vector<syncable::Id> conflicting_ids_;
     std::vector<syncable::Id> successful_ids_;
     std::vector<syncable::Id> encryption_conflict_ids_;
+    bool failed_update_;
   };
 
   // If true, AttemptOneApplication will skip over |entry| and return true.