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

headless/app/headless_shell_switches.cc

Index: headless/app/headless_shell_switches.cc
diff --git a/headless/app/headless_shell_switches.cc b/headless/app/headless_shell_switches.cc
index c748b9b133705dcb76c49fada18e738040cac9c6..ea80e1618705e3aae02196a34470e297492da0a2 100644
--- a/headless/app/headless_shell_switches.cc
+++ b/headless/app/headless_shell_switches.cc
@@ -34,6 +34,13 @@ 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";