Download Service : Added leveldb proto layer

components/download/internal/proto/request.proto

+// Copyright 2017 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.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+package protodb;
+
+message RequestHeader {
+  optional string key = 1;
+  optional string value = 2;
+}
+
+// Stores the HTTP request params associated with a download request.
+message RequestParams {
+  optional string url = 1;
+  optional string method = 2;
+  repeated RequestHeader headers = 3;
+}