Add option --dump-render-tree to content_shell to dump the render tree as text.

content/shell/shell_switches.cc

Index: content/shell/shell_switches.cc
diff --git a/content/shell/shell_switches.cc b/content/shell/shell_switches.cc
new file mode 100644
index 0000000000000000000000000000000000000000..0411cf209ca56b8b352bce077b10b16be91e686d
--- /dev/null
+++ b/content/shell/shell_switches.cc
@@ -0,0 +1,12 @@
+// 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 {
+
+// Request pages to be dumped as text once they finished loading.
+const char kDumpRenderTree[] = "dump-render-tree";
+
+}  // namespace switches