Prevent making real DNS lookups by chrome tests.

net/base/host_resolver.h

 // 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.
 
 #ifndef NET_BASE_HOST_RESOLVER_H_
 #define NET_BASE_HOST_RESOLVER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 41 matching lines @@
   friend class Request;
   scoped_refptr<Request> request_;
   DISALLOW_COPY_AND_ASSIGN(HostResolver);
 };
 
 // A helper class used in unit tests to alter hostname mappings.  See
 // SetHostMapper for details.
 class HostMapper : public base::RefCountedThreadSafe<HostMapper> {
  public:
   virtual ~HostMapper() {}
+
+  // Returns possibly altered hostname, or empty string to simulate
+  // a failed lookup.
   virtual std::string Map(const std::string& host) = 0;
 
  protected:
   // Ask previous host mapper (if set) for mapping of given host.
   std::string MapUsingPrevious(const std::string& host);
 
  private:
   friend class ScopedHostMapper;
 
   // Set mapper to ask when this mapper doesn't want to modify the result.
@@ skipping 16 matching lines @@
 //
 // NOTE: In most cases, you should use ScopedHostMapper instead, which is
 // defined in host_resolver_unittest.h
 //
 HostMapper* SetHostMapper(HostMapper* host_mapper);
 #endif
 
 }  // namespace net
 
 #endif  // NET_BASE_HOST_RESOLVER_H_