Turned UiStrings into a singleton so that the continue window does not depend on ChromotingHost.

remoting/host/it2me_host_user_interface.h

Index: remoting/host/it2me_host_user_interface.h
diff --git a/remoting/host/it2me_host_user_interface.h b/remoting/host/it2me_host_user_interface.h
index 7471aa06383c1f5b958dda56adc7d1bff74a48de..119d072a048504141142a1299249f885436d291a 100644
--- a/remoting/host/it2me_host_user_interface.h
+++ b/remoting/host/it2me_host_user_interface.h
@@ -26,7 +26,8 @@ class It2MeHostUserInterface : public HostUserInterface {
  public:
   It2MeHostUserInterface(
       scoped_refptr<base::SingleThreadTaskRunner> network_task_runner,
-      scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner);
+      scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner,
+      const UiStrings& ui_strings);
   virtual ~It2MeHostUserInterface();
 
   // HostUserInterface overrides.