Move Singleton and related structs to namespace base

extensions/browser/api/test/test_api.h

Index: extensions/browser/api/test/test_api.h
diff --git a/extensions/browser/api/test/test_api.h b/extensions/browser/api/test/test_api.h
index b35ba32f7d08c653ce7a779c423a5238a1041a26..358b4832de1c079ddf46b4aab1dcebb91b37ee72 100644
--- a/extensions/browser/api/test/test_api.h
+++ b/extensions/browser/api/test/test_api.h
@@ -8,9 +8,13 @@
 #include "base/values.h"
 #include "extensions/browser/extension_function.h"
 
+namespace base {
+
 template <typename T>
 struct DefaultSingletonTraits;
 
+}  // namespace base
+
 namespace extensions {
 
 // A function that is only available in tests.
@@ -100,7 +104,7 @@ class TestGetConfigFunction : public TestExtensionFunction {
     const base::DictionaryValue* config_state() { return config_state_; }
 
    private:
-    friend struct DefaultSingletonTraits<TestConfigState>;
+    friend struct base::DefaultSingletonTraits<TestConfigState>;
     TestConfigState();
 
     base::DictionaryValue* config_state_;