Move Singleton and related structs to namespace base

net/quic/crypto/common_cert_set.cc

Index: net/quic/crypto/common_cert_set.cc
diff --git a/net/quic/crypto/common_cert_set.cc b/net/quic/crypto/common_cert_set.cc
index 1a78f1b45030b987c0bea46e2c28ada95b40d463..d4603c71f018e111d05b754aae4a948026b2b491 100644
--- a/net/quic/crypto/common_cert_set.cc
+++ b/net/quic/crypto/common_cert_set.cc
@@ -137,14 +137,14 @@ class CommonCertSetsQUIC : public CommonCertSets {
   }
 
   static CommonCertSetsQUIC* GetInstance() {
-    return Singleton<CommonCertSetsQUIC>::get();
+    return base::Singleton<CommonCertSetsQUIC>::get();
   }
 
  private:
   CommonCertSetsQUIC() {}
   ~CommonCertSetsQUIC() override {}
 
-  friend struct DefaultSingletonTraits<CommonCertSetsQUIC>;
+  friend struct base::DefaultSingletonTraits<CommonCertSetsQUIC>;
   DISALLOW_COPY_AND_ASSIGN(CommonCertSetsQUIC);
 };