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

net/proxy/mojo_proxy_resolver_factory.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_H_
 #define NET_PROXY_MOJO_PROXY_RESOLVER_FACTORY_H_
 
 #include <memory>
 
 #include "base/callback_helpers.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "net/interfaces/host_resolver_service.mojom.h"
 #include "net/interfaces/proxy_resolver_service.mojom.h"
 
 namespace net {
 
 // Factory for connecting to Mojo ProxyResolver services.
 class MojoProxyResolverFactory {
  public:
   // Connect to a new ProxyResolver service using request |req|, using
   // |host_resolver| as the DNS resolver. The return value should be released
   // when the connection to |req| is no longer needed.
   // Note: The connection request |req| may be resolved asynchronously.
   virtual std::unique_ptr<base::ScopedClosureRunner> CreateResolver(
-      const mojo::String& pac_script,
+      const std::string& pac_script,
       mojo::InterfaceRequest<interfaces::ProxyResolver> req,
       interfaces::ProxyResolverFactoryRequestClientPtr client) = 0;
 
  protected:
   virtual ~MojoProxyResolverFactory() = default;
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_MOJO_PROXY_RESOLVER_FACTORY_H_