[Sync] Refactor non-frontend DTC to handle new API properly.

chrome/browser/sync/api/syncable_service_mock.h

Index: chrome/browser/sync/api/syncable_service_mock.h
diff --git a/chrome/browser/sync/api/syncable_service_mock.h b/chrome/browser/sync/api/syncable_service_mock.h
index 2575183fb45f5a0e26484a58e539ffd6f79e716c..dab910d5aee56f305102e4881c23eaa766a090d1 100644
--- a/chrome/browser/sync/api/syncable_service_mock.h
+++ b/chrome/browser/sync/api/syncable_service_mock.h
@@ -7,11 +7,13 @@
 #pragma once
 
 #include "base/location.h"
+#include "base/memory/weak_ptr.h"
 #include "chrome/browser/sync/api/syncable_service.h"
 #include "chrome/browser/sync/api/sync_change.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
-class SyncableServiceMock : public SyncableService {
+class SyncableServiceMock : public SyncableService,
+                            public base::SupportsWeakPtr<SyncableServiceMock> {
  public:
   SyncableServiceMock();
   virtual ~SyncableServiceMock();