Implement cycle window forward/backward by keyboard shortcuts.

ui/aura_shell/shell.cc

Index: ui/aura_shell/shell.cc
diff --git a/ui/aura_shell/shell.cc b/ui/aura_shell/shell.cc
index 87be5acada237f89b6bdc2ee5e3bdd495797c596..51c1b99d51f0f21cec974f84ebe52b84b877f4cf 100644
--- a/ui/aura_shell/shell.cc
+++ b/ui/aura_shell/shell.cc
@@ -4,6 +4,8 @@
 
 #include "ui/aura_shell/shell.h"
 
+#include <algorithm>
+
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "ui/aura/aura_switches.h"
@@ -285,6 +287,21 @@ void Shell::ToggleAppList() {
   app_list_->SetVisible(!app_list_->IsVisible());
 }
 
+// Returns true if the screen is locked.
+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;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Shell, private: