Move Singleton and related structs to namespace base

chrome/browser/ui/views/apps/keyboard_hook_handler.cc

Index: chrome/browser/ui/views/apps/keyboard_hook_handler.cc
diff --git a/chrome/browser/ui/views/apps/keyboard_hook_handler.cc b/chrome/browser/ui/views/apps/keyboard_hook_handler.cc
index 60178f031d76aab80baa8a002d582dcf8ff9ff79..11423db3f89a1cbb607666157241282421373e36 100644
--- a/chrome/browser/ui/views/apps/keyboard_hook_handler.cc
+++ b/chrome/browser/ui/views/apps/keyboard_hook_handler.cc
@@ -16,6 +16,6 @@ void KeyboardHookHandler::Deregister(views::Widget* widget) {
 
 // static
 KeyboardHookHandler* KeyboardHookHandler::GetInstance() {
-  return Singleton<KeyboardHookHandler,
-                   DefaultSingletonTraits<KeyboardHookHandler>>::get();
+  return base::Singleton<KeyboardHookHandler, base::DefaultSingletonTraits<
+                                                  KeyboardHookHandler>>::get();
 }