Check for NULL host_ or frontend_ in the sync_backend_host.

chrome/browser/sync/glue/sync_backend_host.cc

Index: chrome/browser/sync/glue/sync_backend_host.cc
diff --git a/chrome/browser/sync/glue/sync_backend_host.cc b/chrome/browser/sync/glue/sync_backend_host.cc
index d6796292c230fb6af66bd130c79837bbc1c37423..435ff436b8d74babe5118f01c5897da6c41f1809 100644
--- a/chrome/browser/sync/glue/sync_backend_host.cc
+++ b/chrome/browser/sync/glue/sync_backend_host.cc
@@ -538,10 +538,14 @@ void SyncBackendHost::Core::OnInitializationComplete() {
 }
 
 void SyncBackendHost::Core::HandleInitalizationCompletedOnFrontendLoop() {
+  if (!host_)
+    return;
   host_->HandleInitializationCompletedOnFrontendLoop();
 }
 
 void SyncBackendHost::HandleInitializationCompletedOnFrontendLoop() {
+  if (!frontend_)
+    return;
   frontend_->OnBackendInitialized();
 }
 
@@ -598,6 +602,8 @@ void SyncBackendHost::Core::OnStopSyncingPermanently() {
 }
 
 void SyncBackendHost::Core::HandleStopSyncingPermanentlyOnFrontendLoop() {
+  if (!host_ || !host_->frontend_)
+    return;
   host_->frontend_->OnStopSyncingPermanently();
 }