Make the pref_service in TestShellDelegate injectable.

ash/test/test_shell_delegate.h

Index: ash/test/test_shell_delegate.h
diff --git a/ash/test/test_shell_delegate.h b/ash/test/test_shell_delegate.h
index 27f61aa0fd0fbe0faf5daee00d428966d31f0aeb..b56ee14edefc16238633bf538c0c9c0248ee27ed 100644
--- a/ash/test/test_shell_delegate.h
+++ b/ash/test/test_shell_delegate.h
@@ -12,7 +12,7 @@
 #include "ash/test/test_session_state_delegate.h"
 #include "base/macros.h"
 
-class TestingPrefServiceSimple;
+class PrefService;
 
 namespace keyboard {
 class KeyboardUI;
@@ -32,6 +32,10 @@ class TestShellDelegate : public ShellDelegate {
     multi_profiles_enabled_ = multi_profiles_enabled;
   }
 
+  void set_active_user_pref_service(PrefService* pref_service) {
+    active_user_pref_service_ = pref_service;
+  }
+
   // Overridden from ShellDelegate:
   ::service_manager::Connector* GetShellConnector() const override;
   bool IsIncognitoAllowed() const override;
@@ -74,7 +78,7 @@ class TestShellDelegate : public ShellDelegate {
   bool force_maximize_on_first_run_;
   bool touchscreen_enabled_in_local_pref_;
   std::unique_ptr<ShelfInitializer> shelf_initializer_;
-  std::unique_ptr<TestingPrefServiceSimple> pref_service_;
+  PrefService* active_user_pref_service_;  // Not owned.
 
   DISALLOW_COPY_AND_ASSIGN(TestShellDelegate);
 };