[Sync] Replace uses of ObserverListThreadSafe with WeakHandles

chrome/browser/sync/sessions/sync_session_unittest.cc

Index: chrome/browser/sync/sessions/sync_session_unittest.cc
diff --git a/chrome/browser/sync/sessions/sync_session_unittest.cc b/chrome/browser/sync/sessions/sync_session_unittest.cc
index 8c4680244585b2eea45ba2419cae1321c9b6960d..5ee4ac6ab442ddd1dbaa5df2291592ebad693f29 100644
--- a/chrome/browser/sync/sessions/sync_session_unittest.cc
+++ b/chrome/browser/sync/sessions/sync_session_unittest.cc
@@ -7,6 +7,7 @@
 #include "base/compiler_specific.h"
 #include "base/location.h"
 #include "base/memory/ref_counted.h"
+#include "base/message_loop.h"
 #include "chrome/browser/sync/engine/conflict_resolver.h"
 #include "chrome/browser/sync/engine/mock_model_safe_workers.h"
 #include "chrome/browser/sync/engine/syncer_types.h"
@@ -101,6 +102,7 @@ class SyncSessionTest : public testing::Test,
     return request_params;
   }
 
+  MessageLoop message_loop_;
   bool controller_invocations_allowed_;
   scoped_ptr<SyncSession> session_;
   scoped_ptr<SyncSessionContext> context_;