[content shell] run headless when in layout test mode

content/shell/shell_switches.cc

 // Copyright (c) 2012 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 "content/shell/shell_switches.h"
 
 namespace switches {
 
 // Allow access to external pages during layout tests.
 const char kAllowExternalPages[] = "allow-external-pages";
 
 // Check whether all system dependencies for running layout tests are met.
 const char kCheckLayoutTestSysDeps[] = "check-layout-test-sys-deps";
 
 // Tells Content Shell that it's running as a content_browsertest.
 const char kContentBrowserTest[] = "browser-test";
 
 // Makes Content Shell use the given path for its data directory.
 const char kContentShellDataPath[] = "data-path";
 
 // Request pages to be dumped as text once they finished loading.
 const char kDumpRenderTree[] = "dump-render-tree";
 
 // Disables the timeout for layout tests.
 const char kNoTimeout[] = "no-timeout";
 
 // Save results when layout-as-browser tests fail.
 const char kOutputLayoutTestDifferences[] = "output-layout-test-differences";
 
+// Show the content_shell window, even when running in layout test mode.
+const char kShowContentShell[] = "show-content-shell";
+
 }  // namespace switches