DCHECK that ProfileSyncService is created on the UI thread.

chrome/browser/sync/backend_migrator_unittest.cc

Index: chrome/browser/sync/backend_migrator_unittest.cc
diff --git a/chrome/browser/sync/backend_migrator_unittest.cc b/chrome/browser/sync/backend_migrator_unittest.cc
index 7736e8708e555eb0bdc7189f81ff2c48dc689e50..96de473732d3c19a030978465753c8584c8edb11 100644
--- a/chrome/browser/sync/backend_migrator_unittest.cc
+++ b/chrome/browser/sync/backend_migrator_unittest.cc
@@ -5,10 +5,12 @@
 #include "chrome/browser/sync/backend_migrator.h"
 
 #include "base/message_loop/message_loop.h"
+#include "base/run_loop.h"
 #include "base/tracked_objects.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/sync/profile_sync_service_mock.h"
 #include "components/sync_driver/data_type_manager_mock.h"
+#include "content/public/test/test_browser_thread_bundle.h"
 #include "sync/internal_api/public/base/model_type_test_util.h"
 #include "sync/internal_api/public/test/test_user_share.h"
 #include "sync/internal_api/public/write_transaction.h"
@@ -84,7 +86,8 @@ class SyncBackendMigratorTest : public testing::Test {
           requested_types);
       migrator_->OnConfigureDone(result);
     }
-    message_loop_.RunUntilIdle();
+    base::RunLoop run_loop;
+    run_loop.RunUntilIdle();
   }
 
   ProfileSyncService* service() { return &service_; }
@@ -100,7 +103,7 @@ class SyncBackendMigratorTest : public testing::Test {
 
  private:
   scoped_ptr<SyncSessionSnapshot> snap_;
-  base::MessageLoop message_loop_;
+  content::TestBrowserThreadBundle thread_bundle_;

[maniscalco, 2015/02/18 17:03:00]

nit: can you see about making thread_bundle_ the first data member?  I.e. swap
this line with the one above it.  Generally, you want your message loops to be
the first things created and the last ones destroyed in tests.  Actually, is
snap_ used anywhere?  Maybe you can just delete it. 

[maxbogue, 2015/02/18 19:00:06]

Deleted it and the tests still pass.

   syncer::ModelTypeSet preferred_types_;
   TestingProfile profile_;
   NiceMock<ProfileSyncServiceMock> service_;