reapply r70628. It was wrongly blamed for breaking Linux valgrind bots.

chrome/browser/net/connection_tester.cc

Index: chrome/browser/net/connection_tester.cc
diff --git a/chrome/browser/net/connection_tester.cc b/chrome/browser/net/connection_tester.cc
index 18960ebf80490d32c7571ac9d7802b65d26da61f..f23d619fa576a675da141f022ca2b45606c3a8d7 100644
--- a/chrome/browser/net/connection_tester.cc
+++ b/chrome/browser/net/connection_tester.cc
@@ -71,6 +71,7 @@ class ExperimentURLRequestContext : public URLRequestContext {
             dnsrr_resolver_, NULL /* dns_cert_checker */,
             NULL /* ssl_host_info_factory */, proxy_service_,
             ssl_config_service_, http_auth_handler_factory_, NULL, NULL),
+        NULL /* net_log */,
         net::HttpCache::DefaultBackend::InMemory(0));
     // In-memory cookie store.
     cookie_store_ = new net::CookieMonster(NULL, NULL);