Reverting this as it causes browser tests on the Linux ChromiumOS builder to fail.

chrome/browser/sync/profile_sync_service_mock.cc

Index: chrome/browser/sync/profile_sync_service_mock.cc
===================================================================
--- chrome/browser/sync/profile_sync_service_mock.cc	(revision 150390)
+++ chrome/browser/sync/profile_sync_service_mock.cc	(working copy)
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chrome/browser/prefs/pref_service.h"
+#include "chrome/browser/prefs/pref_service_mock_builder.h"
 #include "chrome/browser/prefs/testing_pref_store.h"
 #include "chrome/browser/signin/signin_manager_factory.h"
 #include "chrome/browser/sync/profile_sync_service_mock.h"
@@ -31,7 +31,14 @@
 // static
 TestingProfile* ProfileSyncServiceMock::MakeSignedInTestingProfile() {
   TestingProfile* profile = new TestingProfile();
-  profile->GetPrefs()->SetString(prefs::kGoogleServicesUsername, "foo");
+  TestingPrefStore* user_prefs = new TestingPrefStore();
+  PrefService* prefs = PrefServiceMockBuilder()
+      .WithUserPrefs(user_prefs)
+      .Create();
+  profile->SetPrefService(prefs);
+  // We just blew away our prefs, so reregister them.
+  SigninManagerFactory::GetInstance()->RegisterUserPrefs(prefs);
+  user_prefs->SetString(prefs::kGoogleServicesUsername, "foo");
   return profile;
 }