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

chrome/browser/sync/glue/sync_backend_host.h

Index: chrome/browser/sync/glue/sync_backend_host.h
diff --git a/chrome/browser/sync/glue/sync_backend_host.h b/chrome/browser/sync/glue/sync_backend_host.h
index be1d88a8af0903c1ad0c983cb8d14ca0f1a3fc2b..93382bcc470d6bcbcd7982e835c99bede9e1d3c3 100644
--- a/chrome/browser/sync/glue/sync_backend_host.h
+++ b/chrome/browser/sync/glue/sync_backend_host.h
@@ -24,6 +24,7 @@
 #include "chrome/browser/sync/notifier/sync_notifier_factory.h"
 #include "chrome/browser/sync/protocol/sync_protocol_error.h"
 #include "chrome/browser/sync/syncable/model_type.h"
+#include "chrome/browser/sync/unrecoverable_error_handler.h"
 #include "chrome/browser/sync/util/weak_handle.h"
 #include "chrome/common/net/gaia/google_service_auth_error.h"
 #include "googleurl/src/gurl.h"
@@ -49,7 +50,7 @@ class SyncPrefs;
 // activity.
 // NOTE: All methods will be invoked by a SyncBackendHost on the same thread
 // used to create that SyncBackendHost.
-class SyncFrontend {
+class SyncFrontend : public browser_sync::UnrecoverableErrorHandler {
  public:
   SyncFrontend() {}
 
@@ -293,6 +294,9 @@ class SyncBackendHost {
         const syncable::ModelTypeSet& encrypted_types);
     virtual void OnActionableError(
         const browser_sync::SyncProtocolError& sync_error);
+    virtual void OnUnrecoverableError(
+        const tracked_objects::Location& location,
+        const std::string& message) OVERRIDE;
 
     struct DoInitializeOptions {
       DoInitializeOptions(
@@ -430,6 +434,11 @@ class SyncBackendHost {
     void HandleActionableErrorEventOnFrontendLoop(
         const browser_sync::SyncProtocolError& sync_error);
 
+    // Informs the front end of the unrecoverable error.
+    void HandleUnrecoverableErrorOnFrontendLoop(
+        const tracked_objects::Location& location,
+        const std::string& message);
+
     // Dispatched to from OnAuthError to handle updating frontend UI
     // components.
     void HandleAuthErrorEventOnFrontendLoop(