Make CertVerifier a pure virtual interface.

net/url_request/url_request_test_util.cc

Index: net/url_request/url_request_test_util.cc
diff --git a/net/url_request/url_request_test_util.cc b/net/url_request/url_request_test_util.cc
index 2f3dd6e14c9e50527f475148b4bc23ea585ddf03..d3899dc9286013ced8403721b98765d6984e3599 100644
--- a/net/url_request/url_request_test_util.cc
+++ b/net/url_request/url_request_test_util.cc
@@ -10,6 +10,7 @@
 #include "base/threading/thread.h"
 #include "net/base/default_origin_bound_cert_store.h"
 #include "net/base/host_port_pair.h"
+#include "net/base/multi_threaded_cert_verifier.h"
 #include "net/base/origin_bound_cert_service.h"
 #include "net/http/http_network_session.h"
 #include "net/http/http_server_properties_impl.h"
@@ -110,7 +111,7 @@ void TestURLRequestContext::Init() {
   DCHECK(!initialized_);
   initialized_ = true;
   if (!cert_verifier())
-    context_storage_.set_cert_verifier(new net::CertVerifier);
+    context_storage_.set_cert_verifier(new net::MultiThreadedCertVerifier);
   if (!ftp_transaction_factory()) {
     context_storage_.set_ftp_transaction_factory(
         new net::FtpNetworkLayer(host_resolver()));