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

chrome/browser/prerender/prerender_manager.h

Index: chrome/browser/prerender/prerender_manager.h
diff --git a/chrome/browser/prerender/prerender_manager.h b/chrome/browser/prerender/prerender_manager.h
index f472d368ea1a6246729283b2860994b43001d374..c2d41edc1b30001f9109b9438e61760f7724bd44 100644
--- a/chrome/browser/prerender/prerender_manager.h
+++ b/chrome/browser/prerender/prerender_manager.h
@@ -83,7 +83,10 @@ class PrerenderManager : public content::NotificationObserver,
   enum PrerenderManagerMode {
     PRERENDER_MODE_DISABLED,
     PRERENDER_MODE_ENABLED,
-    PRERENDER_MODE_NOSTATE_PREFETCH
+    PRERENDER_MODE_NOSTATE_PREFETCH,
+    // Like PRERENDER_MODE_DISABLED, but keeps track of pages that would have
+    // been prerendered and records metrics for comparison with other modes.
+    PRERENDER_MODE_SIMPLE_LOAD_EXPERIMENT
   };
 
   // One or more of these flags must be passed to ClearData() to specify just
@@ -222,6 +225,7 @@ class PrerenderManager : public content::NotificationObserver,
   static void SetMode(PrerenderManagerMode mode);
   static bool IsPrerenderingPossible();
   static bool IsNoStatePrefetch();
+  static bool IsSimpleLoadExperiment();
 
   // Query the list of current prerender pages to see if the given web contents
   // is prerendering a page. The optional parameter |origin| is an output