Don't activate a window if screen is locked.

ash/shell.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 "ash/shell.h"
 
 #include <algorithm>
 
 #include "ash/accelerators/accelerator_controller.h"
 #include "ash/accelerators/accelerator_filter.h"
@@ skipping 359 matching lines @@
 
 void Shell::ToggleAppList() {
   if (!app_list_.get())
     app_list_.reset(new internal::AppList);
   app_list_->SetVisible(!app_list_->IsVisible());
 }
 
 bool Shell::IsScreenLocked() const {
   const aura::Window* lock_screen_container = GetContainer(
       internal::kShellWindowId_LockScreenContainer);
-  const aura::Window::Windows& lock_screen_windows =
-      lock_screen_container->children();
-  aura::Window::Windows::const_iterator lock_screen_it =
-      std::find_if(lock_screen_windows.begin(), lock_screen_windows.end(),
-                   std::mem_fun(&aura::Window::IsVisible));
-  if (lock_screen_it != lock_screen_windows.end())
-    return true;
-
-  return false;
+  return lock_screen_container->StopsEventPropagation();
 }
 
 bool Shell::IsModalWindowOpen() const {
   aura::Window* modal_container =
       ash::Shell::GetInstance()->GetContainer(
           internal::kShellWindowId_AlwaysOnTopContainer);
   return !modal_container->children().empty();
 }
 
 views::NonClientFrameView* Shell::CreateDefaultNonClientFrameView(
@@ skipping 16 matching lines @@
       new internal::WorkspaceController(default_container));
   workspace_controller_->SetLauncherModel(launcher_->model());
   default_container->SetEventFilter(
       new internal::DefaultContainerEventFilter(default_container));
   default_container->SetLayoutManager(
       new internal::DefaultContainerLayoutManager(
           workspace_controller_->workspace_manager()));
 }
 
 }  // namespace ash