Make CertVerifier a pure virtual interface.

net/tools/fetch/fetch_client.cc

Index: net/tools/fetch/fetch_client.cc
diff --git a/net/tools/fetch/fetch_client.cc b/net/tools/fetch/fetch_client.cc
index 7b8c7e25c0acf65e7807514608a80dce0d041816..6bbe2d019805878c7e062abd429ac55d947e5920 100644
--- a/net/tools/fetch/fetch_client.cc
+++ b/net/tools/fetch/fetch_client.cc
@@ -13,10 +13,10 @@
 #include "base/metrics/stats_counters.h"
 #include "base/string_number_conversions.h"
 #include "base/string_util.h"
-#include "net/base/cert_verifier.h"
 #include "net/base/completion_callback.h"
 #include "net/base/host_resolver.h"
 #include "net/base/io_buffer.h"
+#include "net/base/multi_threaded_cert_verifier.h"
 #include "net/base/net_errors.h"
 #include "net/base/ssl_config_service_defaults.h"
 #include "net/http/http_auth_handler_factory.h"
@@ -145,7 +145,8 @@ int main(int argc, char** argv) {
                                     net::HostResolver::kDefaultRetryAttempts,
                                     NULL));
 
-  scoped_ptr<net::CertVerifier> cert_verifier(new net::CertVerifier);
+  scoped_ptr<net::CertVerifier> cert_verifier(
+      new net::MultiThreadedCertVerifier);
   scoped_ptr<net::ProxyService> proxy_service(
       net::ProxyService::CreateDirect());
   scoped_refptr<net::SSLConfigService> ssl_config_service(