Convert some NetError[Tab]Helper messages to mojom

chrome/common/network_diagnostics.mojom

+// Copyright 2016 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 mojom;
+
+import "url/mojo/url.mojom";
+
+interface NetworkDiagnostics {
+  RunNetworkDiagnostics(url.mojom.Url failed_url);
+};
+
+interface NetworkDiagnosticsClient {
+  // Tells the renderer whether or not there is a local diagnostics service that
+  // can be run via calls to NetworkDiagnostics::RunNetworkDiagnostics.
+  SetCanShowNetworkDiagnosticsDialog(bool can_show);
+};