Move Singleton and related structs to namespace base

content/browser/gpu/gpu_data_manager_impl.h

Index: content/browser/gpu/gpu_data_manager_impl.h
diff --git a/content/browser/gpu/gpu_data_manager_impl.h b/content/browser/gpu/gpu_data_manager_impl.h
index 3f1d2761c2fc64894fb3a9cffb2404ddd3957341..20df27ab17990d8a0e18c6b763a71a80cef8d781 100644
--- a/content/browser/gpu/gpu_data_manager_impl.h
+++ b/content/browser/gpu/gpu_data_manager_impl.h
@@ -185,7 +185,7 @@ class CONTENT_EXPORT GpuDataManagerImpl
  private:
   friend class GpuDataManagerImplPrivate;
   friend class GpuDataManagerImplPrivateTest;
-  friend struct DefaultSingletonTraits<GpuDataManagerImpl>;
+  friend struct base::DefaultSingletonTraits<GpuDataManagerImpl>;
 
   // It's similar to AutoUnlock, but we want to make it a no-op
   // if the owner GpuDataManagerImpl is null.