Make ChromotingHost::ui_strings() immutable.

remoting/host/chromoting_host.cc

Index: remoting/host/chromoting_host.cc
diff --git a/remoting/host/chromoting_host.cc b/remoting/host/chromoting_host.cc
index 98a2a6ce357de57764febe7d43c4bb9c7e7156c0..dd8299d60f3e9a1a3bf11bc4082f62056d1186ca 100644
--- a/remoting/host/chromoting_host.cc
+++ b/remoting/host/chromoting_host.cc
@@ -361,6 +361,13 @@ void ChromotingHost::PauseSession(bool pause) {
   desktop_environment_->OnPause(!pause);
 }
 
+void ChromotingHost::SetUiStrings(const UiStrings& ui_strings) {
+  DCHECK_EQ(context_->main_message_loop(), MessageLoop::current());
+  DCHECK_EQ(state_, kInitial);
+
+  ui_strings_ = ui_strings;
+}
+
 void ChromotingHost::OnClientDisconnected(ConnectionToClient* connection) {
   DCHECK_EQ(context_->main_message_loop(), MessageLoop::current());