WIP attempt to replace StartWorker/StopWorker IPCs with a new mojo EmbeddedWorker service.

content/common/service_worker/embedded_worker.mojom

+// 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 content;
+
+struct EmbeddedWorkerStartWorkerParams {
+  int32 embedded_worker_id;
+  int64 service_worker_version_id;
+  string scope;
+  string script_url;
+  int32 worker_devtools_agent_route_id;
+  bool pause_after_download;
+  bool wait_for_debugger;
+  int32 v8_cache_options; // content::V8CacheOptions
+};
+
+interface EmbeddedWorker {
+  Initialize(EmbeddedWorkerStartWorkerParams params);
+};