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

chrome/browser/sync/engine/model_changing_syncer_command.cc

Index: chrome/browser/sync/engine/model_changing_syncer_command.cc
diff --git a/chrome/browser/sync/engine/model_changing_syncer_command.cc b/chrome/browser/sync/engine/model_changing_syncer_command.cc
index 797f795f96bd08580aeb6ac466459e231e7c7763..71f9a9a2ef005749cfb7ab8bbabf109df3d9487b 100644
--- a/chrome/browser/sync/engine/model_changing_syncer_command.cc
+++ b/chrome/browser/sync/engine/model_changing_syncer_command.cc
@@ -8,8 +8,10 @@
 #include "chrome/browser/sync/engine/model_safe_worker.h"
 #include "chrome/browser/sync/sessions/status_controller.h"
 #include "chrome/browser/sync/sessions/sync_session.h"
+#include "chrome/browser/sync/sessions/unrecoverable_error_info.h"
 
 namespace browser_sync {
+using sessions::UnrecoverableErrorInfo;
 
 void ModelChangingSyncerCommand::ExecuteImpl(sessions::SyncSession* session) {
   work_session_ = session;
@@ -45,9 +47,14 @@ void ModelChangingSyncerCommand::ExecuteImpl(sessions::SyncSession* session) {
 
     sessions::StatusController* status = work_session_->status_controller();
     sessions::ScopedModelSafeGroupRestriction r(status, group);
-    scoped_ptr<Callback0::Type> c(NewCallback(this,
+    scoped_ptr<Callback1<UnrecoverableErrorInfo*>::Type> c(
+        NewCallback(this,
         &ModelChangingSyncerCommand::StartChangingModel));
-    worker->DoWorkAndWaitUntilDone(c.get());
+    UnrecoverableErrorInfo error_info;
+    worker->DoWorkAndWaitUntilDone(c.get(), &error_info);
+
+    // TODO(lipalani): Check if there is an unrecoverable error from error_info
+    // and do apropriate actions.
   }
 }