Add GetMimeTypeFromFile to Mojo's network service.

mojo/services/network/public/interfaces/network_service.mojom

 // Copyright 2014 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.
 
 module mojo;
 
 import "network/public/interfaces/cookie_store.mojom";
 import "network/public/interfaces/http_server.mojom";
 import "network/public/interfaces/net_address.mojom";
 import "network/public/interfaces/network_error.mojom";
@@ skipping 51 matching lines @@
   //
   // The local address can specify 0 for the port to specify that the OS should
   // pick an available port for the given address, or it can pass 0 for the
   // address and port for the OS to pick both the local address and port. In
   // all success cases, the resulting local address will be passed to the
   // callback as bound_to.
   CreateHttpServer(NetAddress local_address,
                    HttpServerDelegate delegate)
       => (NetworkError result,
           NetAddress? bound_to);
+
+  // Get the mime type (if any) that is associated with the given file.
+  GetMimeTypeFromFile(string file_path) => (string mime_type);
 };