Prevent making real DNS lookups by chrome tests.

net/base/host_resolver.cc

 // Copyright (c) 2006-2008 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.
 
 #include "net/base/host_resolver.h"
 
 #if defined(OS_WIN)
 #include <ws2tcpip.h>
 #include <wspiapi.h>  // Needed for Win2k compat.
 #elif defined(OS_POSIX)
@@ skipping 34 matching lines @@
 
   // Restrict result set to only this socket type to avoid duplicates.
   hints.ai_socktype = SOCK_STREAM;
 
   int err = getaddrinfo(host.c_str(), port.c_str(), &hints, out);
   return err ? ERR_NAME_NOT_RESOLVED : OK;
 }
 
 static int ResolveAddrInfo(HostMapper* mapper, const std::string& host,
                            const std::string& port, struct addrinfo** out) {
-  int rv;
   if (mapper) {
-    rv = HostResolverProc(mapper->Map(host), port, out);
+    std::string mapped_host = mapper->Map(host);
+
+    if (mapped_host.empty())
+      return ERR_NAME_NOT_RESOLVED;
+
+    return HostResolverProc(mapped_host, port, out);
   } else {
-    rv = HostResolverProc(host, port, out);
+    return HostResolverProc(host, port, out);
   }
-  return rv;
 }
 
 //-----------------------------------------------------------------------------
 
 class HostResolver::Request :
     public base::RefCountedThreadSafe<HostResolver::Request> {
  public:
   Request(HostResolver* resolver,
           const std::string& host,
           const std::string& port,
@@ skipping 124 matching lines @@
           NewRunnableMethod(request_.get(), &Request::DoLookup), true)) {
     NOTREACHED();
     request_ = NULL;
     return ERR_FAILED;
   }
 
   return ERR_IO_PENDING;
 }
 
 }  // namespace net