[headless] Make browser service manifest overlay configurable.

headless/lib/browser/headless_content_browser_client.cc

 // 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.
 
 #include "headless/lib/browser/headless_content_browser_client.h"
 
 #include <memory>
 
 #include "base/callback.h"
 #include "base/json/json_reader.h"
@@ skipping 38 matching lines @@
 }
 
 content::DevToolsManagerDelegate*
 HeadlessContentBrowserClient::GetDevToolsManagerDelegate() {
   return new HeadlessDevToolsManagerDelegate(browser_->GetWeakPtr());
 }
 
 std::unique_ptr<base::Value>
 HeadlessContentBrowserClient::GetServiceManifestOverlay(
     const std::string& name) {
-  if (name != content::kBrowserServiceName)
+  if (name != content::kBrowserServiceName ||
+      !browser_->options()->mojo_service_manifest_resource_id)
     return nullptr;
+
   base::StringPiece manifest_contents =
       ui::ResourceBundle::GetSharedInstance().GetRawDataResource(
-          IDR_HEADLESS_BROWSER_MANIFEST_OVERLAY);
+          browser_->options()->mojo_service_manifest_resource_id);
   return base::JSONReader::Read(manifest_contents);
 }
 
 }  // namespace headless