Adds a --deterministic-fetch flag 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 a0afc6943108d3363719591f3b72e49d7d27e8ad..c67b5df5a6b42ce0cd40ea487ebcf87bbd865611 100644
--- a/headless/app/headless_shell_switches.cc
+++ b/headless/app/headless_shell_switches.cc
@@ -7,6 +7,11 @@
 namespace headless {
 namespace switches {
 
+// Instructs headless_shell to cause network fetches to complete in order of
+// creation. This removes a significant source of network related
+// non-determinism at the cost of slower page loads.
+const char kDeterministicFetch[] = "deterministic-fetch";
+
 // Instructs headless_shell to print document.body.innerHTML to stdout.
 const char kDumpDom[] = "dump-dom";