Add unit test for using literals namespaces

Author: mattyclarkson

cpplint_unittest.py

@@ -2923,6 +2923,10 @@ def DoTest(self, lines):
     DoTest(self, ['', '', '', 'using namespace foo;'])
     DoTest(self, ['// hello', 'using namespace foo;'])
 
+  def testUsingLiteralsNamespaces(self):
+    self.TestLint('using namespace std::literals;', '')
+    self.TestLint('using namespace std::literals::chrono_literals;', '')
+
   def testNewlineAtEOF(self):
     def DoTest(self, data, is_missing_eof):
       error_collector = ErrorCollector(self.assert_)