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

net/proxy/in_process_mojo_proxy_resolver_factory.h

Index: net/proxy/in_process_mojo_proxy_resolver_factory.h
diff --git a/net/proxy/in_process_mojo_proxy_resolver_factory.h b/net/proxy/in_process_mojo_proxy_resolver_factory.h
index b5ccb101439db027e6c42bc8a6d70e548ed9007a..d7b7265388f8dadc5db54508dbdad0dc3f9016c8 100644
--- a/net/proxy/in_process_mojo_proxy_resolver_factory.h
+++ b/net/proxy/in_process_mojo_proxy_resolver_factory.h
@@ -24,7 +24,7 @@ class InProcessMojoProxyResolverFactory : public MojoProxyResolverFactory {
 
   // Overridden from MojoProxyResolverFactory:
   std::unique_ptr<base::ScopedClosureRunner> CreateResolver(
-      const mojo::String& pac_script,
+      const std::string& pac_script,
       mojo::InterfaceRequest<interfaces::ProxyResolver> req,
       interfaces::ProxyResolverFactoryRequestClientPtr client) override;