Enforce the RemoteAccessHostRequireCurtain policy on all platforms.

remoting/host/curtain_mode_win.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "remoting/host/curtain_mode.h"
 
 #include "base/logging.h"
 
 namespace remoting {
 
 class CurtainModeWin : public CurtainMode {
  public:
-  CurtainModeWin() {}
+  CurtainModeWin(const base::Closure& on_error) : on_error_(on_error) {}
   // Overriden from CurtainMode.
   virtual void SetActivated(bool activated) OVERRIDE {
-    NOTIMPLEMENTED();
+    // Curtain-mode is not currently implemented for Windows.
+    if (activated) {
+      on_error_.Run();
+    }
   }
 
  private:
+  base::Closure on_error_;
+
   DISALLOW_COPY_AND_ASSIGN(CurtainModeWin);
 };
 
 // static
 scoped_ptr<CurtainMode> CurtainMode::Create(
     const base::Closure& on_session_activate,
     const base::Closure& on_error) {
   return scoped_ptr<CurtainMode>(
-      new CurtainModeWin());
+      new CurtainModeWin(on_error));
 }
 
 }  // namespace remoting