[gardening] C++ gardening: Terminate namespaces, fix argument names, ...

Changes:
* Terminate all namespaces with the correct closing comment.
* Make sure argument names in comments match the corresponding parameter name.
* Remove redundant get() calls on smart pointers.
* Prefer using "override" or "final" instead of "virtual". Remove "virtual" where appropriate.

unittests/Basic/PrefixMapTest.cpp

@@ -100,7 +100,7 @@ struct Tester {
   }
 };
 
-}
+} // end anonymous namespace
 
 TEST(PrefixMapTest, Insert) {
   PrefixMap<char, int> map;