Move Singleton and related structs to namespace base

content/child/child_io_surface_manager_mac.cc

Index: content/child/child_io_surface_manager_mac.cc
diff --git a/content/child/child_io_surface_manager_mac.cc b/content/child/child_io_surface_manager_mac.cc
index 71980b77bbd2e721d32946a5ea05a38510de0610..fb4ef9ac6524992b20166de6be75ca9ccf1f3b0c 100644
--- a/content/child/child_io_surface_manager_mac.cc
+++ b/content/child/child_io_surface_manager_mac.cc
@@ -11,8 +11,9 @@ namespace content {
 
 // static
 ChildIOSurfaceManager* ChildIOSurfaceManager::GetInstance() {
-  return Singleton<ChildIOSurfaceManager,
-                   LeakySingletonTraits<ChildIOSurfaceManager>>::get();
+  return base::Singleton<
+      ChildIOSurfaceManager,
+      base::LeakySingletonTraits<ChildIOSurfaceManager>>::get();
 }
 
 bool ChildIOSurfaceManager::RegisterIOSurface(IOSurfaceId io_surface_id,