Use std::string instead of mojo::String in //net.

net/proxy/mojo_proxy_resolver_factory_impl.h

 // Copyright 2015 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_PROXY_MOJO_PROXY_RESOLVER_FACTORY_IMPL_H_
 #define NET_PROXY_MOJO_PROXY_RESOLVER_FACTORY_IMPL_H_
 
 #include <map>
 
 #include "base/callback.h"
@@ skipping 11 matching lines @@
   explicit MojoProxyResolverFactoryImpl(
       std::unique_ptr<ProxyResolverV8TracingFactory> proxy_resolver_factory);
 
   ~MojoProxyResolverFactoryImpl() override;
 
  private:
   class Job;
 
   // interfaces::ProxyResolverFactory override.
   void CreateResolver(
-      const mojo::String& pac_script,
+      const std::string& pac_script,
       interfaces::ProxyResolverRequest request,
       interfaces::ProxyResolverFactoryRequestClientPtr client) override;
 
   void RemoveJob(Job* job);
 
   const std::unique_ptr<ProxyResolverV8TracingFactory>
       proxy_resolver_impl_factory_;
 
   std::map<Job*, std::unique_ptr<Job>> jobs_;
 
   DISALLOW_COPY_AND_ASSIGN(MojoProxyResolverFactoryImpl);
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_MOJO_PROXY_RESOLVER_FACTORY_IMPL_H_