The login dialog was being opened with the main browser window as a parent in...

chrome/test/live_sync/profile_sync_service_test_harness.cc

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 #ifdef CHROME_PERSONALIZATION
 
 #include "base/message_loop.h"
 #include "chrome/browser/browser.h"
 #include "chrome/browser/tab_contents/tab_contents.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/pref_service.h"
@@ skipping 100 matching lines @@
   // Ensure the profile has enough prefs registered for use by sync.
   if (!p->GetPrefs()->IsPrefRegistered(prefs::kAcceptLanguages))
     TabContents::RegisterUserPrefs(p->GetPrefs());
   if (!p->GetPrefs()->IsPrefRegistered(prefs::kCookieBehavior))
     Browser::RegisterUserPrefs(p->GetPrefs());
 }
 
 bool ProfileSyncServiceTestHarness::SetupSync() {
   service_ = profile_->GetProfileSyncService();
   service_->SetSyncSetupCompleted();
-  service_->EnableForUser();
+  service_->EnableForUser(NULL);
 
   // Needed to avoid showing the login dialog. Well aware this is egregious.
   service_->expecting_first_run_auth_needed_event_ = false;
   service_->AddObserver(this);
   return WaitForServiceInit();
 }
 
 void ProfileSyncServiceTestHarness::SignalStateCompleteWithNextState(
     WaitState next_state) {
 
@@ skipping 112 matching lines @@
   // Wait for the OnBackendInitialized callback.
   service_->backend()->Authenticate(username_, password_);
   EXPECT_EQ(wait_state_, WAITING_FOR_READY_TO_PROCESS_CHANGES);
   if (!AwaitStatusChangeWithTimeout(30, "Waiting on backend initialization.")) {
     return false;
   }
   return service_->sync_initialized();
 }
 
 #endif  // CHROME_PERSONALIZATION