[Prerender] Add a "SimpleLoad" mode to be used as a comparison reference

chrome/browser/prerender/prerender_field_trial.cc

Index: chrome/browser/prerender/prerender_field_trial.cc
diff --git a/chrome/browser/prerender/prerender_field_trial.cc b/chrome/browser/prerender/prerender_field_trial.cc
index fd26ce8dc529126c87a624c175601e1728ca6fee..a726394b3f61bfbfd140f113c93fa818a43328e1 100644
--- a/chrome/browser/prerender/prerender_field_trial.cc
+++ b/chrome/browser/prerender/prerender_field_trial.cc
@@ -30,6 +30,8 @@ void ConfigurePrerender(const base::CommandLine& command_line) {
       // The empty string means the option was provided with no value, and that
       // means enable.
       mode = PrerenderManager::PRERENDER_MODE_ENABLED;
+    } else if (switch_value == switches::kPrerenderModeSwitchValueSimpleLoad) {
+      mode = PrerenderManager::PRERENDER_MODE_SIMPLE_LOAD_EXPERIMENT;
     } else {
       mode = PrerenderManager::PRERENDER_MODE_DISABLED;
       LOG(ERROR) << "Invalid --prerender option received on command line: "