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

base/memory/weak_ptr_unittest.nc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // 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 {
 
 struct Producer : SupportsWeakPtr<Producer> {};
 struct DerivedProducer : Producer {};
 struct OtherDerivedProducer : Producer {};
 struct MultiplyDerivedProducer : Producer,
                                  SupportsWeakPtr<MultiplyDerivedProducer> {};
 struct Unrelated {};
@@ skipping 114 matching lines @@
 #elif defined(NCTEST_AMBIGUOUS_ANCESTORS)  // [r"fatal error: ambiguous conversion from derived class 'base::MultiplyDerivedProducer' to base class 'base::internal::SupportsWeakPtrBase':"]
 
 void WontCompile() {
   MultiplyDerivedProducer f;
   WeakPtr<MultiplyDerivedProducer> ptr = AsWeakPtr(&f);
 }
 
 #endif
 
 }