Describe .nc files as "No Compile Test" suites and link doc.

base/memory/weak_ptr_unittest.nc

Index: base/memory/weak_ptr_unittest.nc
diff --git a/base/memory/weak_ptr_unittest.nc b/base/memory/weak_ptr_unittest.nc
index 2ab428d2abe8a3e48eda59fa65e7efe5cae648dd..8486ff9c26a0db115b62795720e5e55b979836b0 100644
--- a/base/memory/weak_ptr_unittest.nc
+++ b/base/memory/weak_ptr_unittest.nc
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// This is a "No Compile Test" suite.
+// http://dev.chromium.org/developers/testing/no-compile-tests
+
 #include "base/memory/weak_ptr.h"
 
 namespace base {