Its possible for sync to be suppressed before the user attempts one-click

chrome/browser/ui/sync/one_click_signin_sync_starter.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/ui/sync/one_click_signin_sync_starter.h"
 
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/signin/signin_manager.h"
 #include "chrome/browser/signin/signin_manager_factory.h"
 #include "chrome/browser/sync/profile_sync_service.h"
 #include "chrome/browser/sync/profile_sync_service_factory.h"
+#include "chrome/browser/sync/sync_prefs.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/webui/signin/login_ui_service.h"
 #include "chrome/browser/ui/webui/signin/login_ui_service_factory.h"
 
 OneClickSigninSyncStarter::OneClickSigninSyncStarter(
     Browser* browser,
     const std::string& session_index,
     const std::string& email,
     const std::string& password,
     StartSyncMode start_mode)
     : browser_(browser),
       signin_tracker_(browser_->profile(), this),
       start_mode_(start_mode) {
   DCHECK(browser_);
 
+  // Let the sync service know that setup is in progress so it doesn't start
+  // syncing until the user has finished any configuration.
   ProfileSyncService* profile_sync_service =
       ProfileSyncServiceFactory::GetForProfile(browser_->profile());
-  // Let the sync service know that setup is in progress so it doesn't start
-  // syncing until the user has finished any configuration.
   profile_sync_service->SetSetupInProgress(true);
+
+  // Make sure the syncing is not suppressed, otherwise the SigninManager
+  // will not be able to compelte sucessfully.
+  browser_sync::SyncPrefs sync_prefs(browser_->profile()->GetPrefs());
+  sync_prefs.SetStartSuppressed(false);
+
   SigninManager* manager = SigninManagerFactory::GetForProfile(
       browser_->profile());
   manager->StartSignInWithCredentials(session_index, email, password);
 }
 
 OneClickSigninSyncStarter::~OneClickSigninSyncStarter() {
 }
 
 void OneClickSigninSyncStarter::GaiaCredentialsValid() {
 }
 
 void OneClickSigninSyncStarter::SigninFailed(
     const GoogleServiceAuthError& error) {
   ProfileSyncService* profile_sync_service =
       ProfileSyncServiceFactory::GetForProfile(browser_->profile());
   profile_sync_service->SetSetupInProgress(false);
   delete this;
 }
 
 void OneClickSigninSyncStarter::SigninSuccess() {
   ProfileSyncService* profile_sync_service =
       ProfileSyncServiceFactory::GetForProfile(browser_->profile());
 
   if (start_mode_ == SYNC_WITH_DEFAULT_SETTINGS) {
     // Just kick off the sync machine, no need to configure it first.
     profile_sync_service->SetSyncSetupCompleted();
     profile_sync_service->SetSetupInProgress(false);
-    profile_sync_service->UnsuppressAndStart();
   } else {
     // Give the user a chance to configure things. We don't clear the
     // ProfileSyncService::setup_in_progress flag because we don't want sync
     // to start up until after the configure UI is displayed (the configure UI
     // will clear the flag when the user is done setting up sync).
     LoginUIServiceFactory::GetForProfile(browser_->profile())->ShowLoginUI(
         browser_);
   }
 
   delete this;
 }