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

remoting/host/host_user_interface.h

Index: remoting/host/host_user_interface.h
diff --git a/remoting/host/host_user_interface.h b/remoting/host/host_user_interface.h
index 3a89a064a9fc64a07919e39f3ed6d6ddaa4b8df6..d22cb6155937e2f38958d892ddff1640a008e654 100644
--- a/remoting/host/host_user_interface.h
+++ b/remoting/host/host_user_interface.h
@@ -14,6 +14,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "remoting/host/host_status_observer.h"
+#include "remoting/host/ui_strings.h"
 
 namespace base {
 class SingleThreadTaskRunner;
@@ -29,7 +30,8 @@ class HostUserInterface : public HostStatusObserver {
  public:
   HostUserInterface(
       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 ~HostUserInterface();
 
   // Initialize the OS-specific UI objects.
@@ -56,6 +58,8 @@ class HostUserInterface : public HostStatusObserver {
   }
   ChromotingHost* get_host() const { return host_; }
 
+  const UiStrings& ui_strings() const { return ui_strings_; }
+
   base::SingleThreadTaskRunner* network_task_runner() const;
   base::SingleThreadTaskRunner* ui_task_runner() const;
 
@@ -97,6 +101,9 @@ class HostUserInterface : public HostStatusObserver {
 
   bool is_monitoring_local_inputs_;
 
+  // TODO(alexeypa): move |ui_strings_| to DesktopEnvironmentFactory.
+  UiStrings ui_strings_;
+
   // WeakPtr used to avoid tasks accessing the client after it is deleted.
   base::WeakPtrFactory<HostUserInterface> weak_factory_;
   base::WeakPtr<HostUserInterface> weak_ptr_;