Introduce Http{Request,Response} mojom structs.

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

Index: mojo/services/network/public/interfaces/http_message.mojom
diff --git a/mojo/services/network/public/interfaces/http_message.mojom b/mojo/services/network/public/interfaces/http_message.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..b89ba843c948a0eccfdf697dc348c3e5c5adc93f
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+++ b/mojo/services/network/public/interfaces/http_message.mojom
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+// 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.
+
+module mojo;
+
+struct HttpHeader {
+  string name;
+  string value;
+};
+
+struct HttpRequest {
+  string method = "GET";
+  string url;
+  array<HttpHeader>? headers;
+  handle<data_pipe_consumer>? body;
+};
+
+struct HttpResponse {
+  uint32 status_code = 200;
+  array<HttpHeader>? headers;
+  handle<data_pipe_consumer>? body;
+};