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

content/shell/shell_render_view_host_observer.cc

Index: content/shell/shell_render_view_host_observer.cc
diff --git a/content/shell/shell_render_view_host_observer.cc b/content/shell/shell_render_view_host_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f6138514f10ecc729c32d575e0ccbbcdc841a43e
--- /dev/null
+++ b/content/shell/shell_render_view_host_observer.cc
@@ -0,0 +1,35 @@
+// 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_render_view_host_observer.h"
+
+#include <iostream>
+
+#include "content/shell/shell_messages.h"
+
+namespace content {
+
+ShellRenderViewHostObserver::ShellRenderViewHostObserver(
+    RenderViewHost* render_view_host)
+    : RenderViewHostObserver(render_view_host) {
+}
+
+ShellRenderViewHostObserver::~ShellRenderViewHostObserver() {
+}
+
+bool ShellRenderViewHostObserver::OnMessageReceived(
+    const IPC::Message& message) {
+  bool handled = true;
+  IPC_BEGIN_MESSAGE_MAP(ShellRenderViewHostObserver, message)
+    IPC_MESSAGE_HANDLER(ShellViewHostMsg_TextDump, OnTextDump)
+    IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP()
+  return handled;
+}
+
+void ShellRenderViewHostObserver::OnTextDump(const std::string& dump) {
+  std::cout << dump;
+}
+
+}  // namespace content