Make CertVerifier a pure virtual interface.

net/tools/fetch/fetch_client.cc

Index: net/tools/fetch/fetch_client.cc
===================================================================
--- net/tools/fetch/fetch_client.cc	(revision 128056)
+++ net/tools/fetch/fetch_client.cc	(working copy)
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -145,7 +145,8 @@
                                     net::HostResolver::kDefaultRetryAttempts,
                                     NULL));
 
-  scoped_ptr<net::CertVerifier> cert_verifier(new net::CertVerifier);
+  scoped_ptr<net::CertVerifier> cert_verifier(
+      net::CertVerifier::CreateDefault());
   scoped_ptr<net::ProxyService> proxy_service(
       net::ProxyService::CreateDirect());
   scoped_refptr<net::SSLConfigService> ssl_config_service(