Move Singleton and related structs to namespace base

ui/events/x/events_x.cc

Index: ui/events/x/events_x.cc
diff --git a/ui/events/x/events_x.cc b/ui/events/x/events_x.cc
index 64da7ca6c8626085e4308056c225f829659c9a1f..d9dec447e71e48a8e224a1e0ca68413d218659a3 100644
--- a/ui/events/x/events_x.cc
+++ b/ui/events/x/events_x.cc
@@ -41,7 +41,7 @@ const int kMaxWheelButton = 7;
 class XModifierStateWatcher{
  public:
   static XModifierStateWatcher* GetInstance() {
-    return Singleton<XModifierStateWatcher>::get();
+    return base::Singleton<XModifierStateWatcher>::get();
   }
 
   int StateFromKeyboardCode(ui::KeyboardCode keyboard_code) {
@@ -100,7 +100,7 @@ class XModifierStateWatcher{
   unsigned int state() { return state_; }
 
  private:
-  friend struct DefaultSingletonTraits<XModifierStateWatcher>;
+  friend struct base::DefaultSingletonTraits<XModifierStateWatcher>;
 
   XModifierStateWatcher() : state_(0) { }