Add Page.stopLoading to devtools and --timeout switch 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 18cf95d3e1b7c50edc088adb40efc2b01ad11810..392c5f7e0d091c97e39c4900ac5c8ce233b9062f 100644
--- a/headless/app/headless_shell_switches.cc
+++ b/headless/app/headless_shell_switches.cc
@@ -35,6 +35,10 @@ const char kRepl[] = "repl";
 // Save a screenshot of the loaded page.
 const char kScreenshot[] = "screenshot";
 
+// Issues a stop after the specified number of milliseconds.  This cancels all
+// navigation and causes the DOMContentLoaded event to fire.
+const char kTimeout[] = "timeout";
+
 // Sets the GL implementation to use. Use a blank string to disable GL
 // rendering.
 const char kUseGL[] = "use-gl";