[content shell] run headless when in layout test mode

content/shell/shell.h

 // 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.
 
 #ifndef CONTENT_SHELL_SHELL_H_
 #define CONTENT_SHELL_SHELL_H_
 
 
 #include <vector>
 
@@ skipping 224 matching lines @@
   int content_height_;
 #elif defined(OS_ANDROID)
   base::android::ScopedJavaGlobalRef<jobject> java_object_;
 #elif defined(USE_AURA)
   static aura::client::StackingClient* stacking_client_;
   static views::ViewsDelegate* views_delegate_;
 
   views::Widget* window_widget_;
 #endif
 
+  bool headless_;
+
   // A container of all the open windows. We use a vector so we can keep track
   // of ordering.
   static std::vector<Shell*> windows_;
 
   static base::Callback<void(Shell*)> shell_created_callback_;
 
   // True if the destructur of Shell should post a quit closure on the current
   // message loop if the destructed Shell object was the last one.
   static bool quit_message_loop_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_SHELL_SHELL_H_