[headless] Make browser service manifest overlay configurable.

headless/test/headless_test_launcher.cc

 // 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.
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/sys_info.h"
 #include "content/public/test/content_test_suite_base.h"
@@ skipping 29 matching lines @@
   }
 
   bool AdjustChildProcessCommandLine(
       base::CommandLine* command_line,
       const base::FilePath& temp_data_dir) override {
     return true;
   }
 
  protected:
   content::ContentMainDelegate* CreateContentMainDelegate() override {
-    // Use HeadlessBrowserTest::SetBrowserOptions to override these defaults.
+    // Use HeadlessBrowserTest::options() or HeadlessBrowserContextOptions to
+    // modify these defaults.
     HeadlessBrowser::Options::Builder options_builder;
     std::unique_ptr<HeadlessBrowserImpl> browser(
         new HeadlessBrowserImplForTest(options_builder.Build()));
     return new HeadlessContentMainDelegate(std::move(browser));
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(HeadlessTestLauncherDelegate);
 };
 
 }  // namespace
 }  // namespace headless
 
 int main(int argc, char** argv) {
   int default_jobs = std::max(1, base::SysInfo::NumberOfProcessors() / 2);
   headless::HeadlessTestLauncherDelegate launcher_delegate;
   return LaunchTests(&launcher_delegate, default_jobs, argc, argv);
 }