sync: null-check the Directory ChannelHookup before adding a new observer so we don't add observers twice.

BUG=46596
TEST=on a debug / unofficial build, re-login to sync (e.g. using --invalidate-sync-login). browser shouldn't crash.

Review URL: http://codereview.chromium.org/2799007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@49855 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 6 insertions, 1 deletions

diff --git a/chrome/browser/sync/engine/syncapi.cc b/chrome/browser/sync/engine/syncapi.cc
index 1a2da8b..754ddae 100644
--- a/chrome/browser/sync/engine/syncapi.cc
+++ b/chrome/browser/sync/engine/syncapi.cc
@@ -1798,7 +1798,12 @@ void SyncManager::SyncInternal::HandleAuthWatcherEvent(
                         << "up directory change event listener!";
           return;
         }
-        dir_change_hookup_.reset(lookup->AddChangeObserver(this));
+
+        // Note that we can end up here multiple times, for example if the
+        // user had to re-login and we got a second AUTH_SUCCEEDED event. Take
+        // care not to add ourselves as an observer a second time.
+        if (!dir_change_hookup_.get())
+          dir_change_hookup_.reset(lookup->AddChangeObserver(this));
       }
       if (InitialSyncEndedForAllEnabledTypes())
         MarkAndNotifyInitializationComplete();