[Sync] Return nullptr for OpenTabsUIDelegate when PROXY_TABS is disabled.

chrome/browser/extensions/api/sessions/sessions_apitest.cc

Index: chrome/browser/extensions/api/sessions/sessions_apitest.cc
diff --git a/chrome/browser/extensions/api/sessions/sessions_apitest.cc b/chrome/browser/extensions/api/sessions/sessions_apitest.cc
index 906ea81386860675ee202bf03ac5a2335bba7da4..9abe2efa2d991a9ef631740997c0bd017f49b3a6 100644
--- a/chrome/browser/extensions/api/sessions/sessions_apitest.cc
+++ b/chrome/browser/extensions/api/sessions/sessions_apitest.cc
@@ -217,11 +217,12 @@ void ExtensionSessionsTest::CreateTestProfileSyncService() {
           ProfileSyncServiceFactory::GetInstance()->SetTestingFactoryAndUse(
               profile, &ExtensionSessionsTest::BuildProfileSyncService));
 
-  syncer::ModelTypeSet preferred_types;
-  preferred_types.Put(syncer::SESSIONS);
+  syncer::ModelTypeSet preferred_types(syncer::SESSIONS, syncer::PROXY_TABS);
   GoogleServiceAuthError no_error(GoogleServiceAuthError::NONE);
   ON_CALL(*service, IsDataTypeControllerRunning(syncer::SESSIONS))
       .WillByDefault(testing::Return(true));
+  ON_CALL(*service, IsDataTypeControllerRunning(syncer::PROXY_TABS))
+      .WillByDefault(testing::Return(true));
   ON_CALL(*service, GetRegisteredDataTypes())
       .WillByDefault(testing::Return(syncer::UserTypes()));
   ON_CALL(*service, GetPreferredDataTypes()).WillByDefault(