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

content/shell/shell_switches.h

Index: content/shell/shell_switches.h
diff --git a/content/shell/shell_switches.h b/content/shell/shell_switches.h
new file mode 100644
index 0000000000000000000000000000000000000000..9e4e83884a7770176fecf838e153ec6d7247ff32
--- /dev/null
+++ b/content/shell/shell_switches.h
@@ -0,0 +1,17 @@
+// 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.
+
+// Defines all the "content_shell" command-line switches.
+
+#ifndef CONTENT_SHELL_SHELL_SWITCHES_H_
+#define CONTENT_SHELL_SHELL_SWITCHES_H_
+#pragma once
+
+namespace switches {
+
+extern const char kDumpRenderTree[];
+
+}  // namespace switches
+
+#endif  // CONTENT_SHELL_SHELL_SWITCHES_H_