Add a --virtual-time-budget option to headless_shell

headless/app/headless_shell_switches.cc

 // Copyright 2016 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 "headless/app/headless_shell_switches.h"
 
 namespace headless {
 namespace switches {
 
 // Instructs headless_shell to print document.body.innerHTML to stdout.
@@ skipping 16 matching lines @@
 // Save a screenshot of the loaded page.
 const char kScreenshot[] = "screenshot";
 
 // Sets the GL implementation to use. Use a blank string to disable GL
 // rendering.
 const char kUseGL[] = "use-gl";
 
 // Directory where the browser stores the user profile.
 const char kUserDataDir[] = "user-data-dir";
 
+// Whether or not a virtual time limit should be used to decide when the page is
+// ready.  The idea being that the renderer's view of time is suspended while
+// there are network requests pending and its then able to fast forwards timers
+// until the virtual time threshold is reached at which point the page is deemed
+// ready.
+const char kVirtualTime[] = "virtual-time";
+
 // Sets the initial window size. Provided as string in the format "800x600".
 const char kWindowSize[] = "window-size";
 
 }  // namespace switches
 }  // namespace headless