Fix prerender histograms for multiple prerender case.

chrome/browser/prerender/prerender_origin.cc

Index: chrome/browser/prerender/prerender_origin.cc
diff --git a/chrome/browser/prerender/prerender_origin.cc b/chrome/browser/prerender/prerender_origin.cc
index 084120dd2b18a212af3c62eeee8262a3addd25e1..d22a3adbd39350ff9a9a65e916ad97ef6c6dd785 100644
--- a/chrome/browser/prerender/prerender_origin.cc
+++ b/chrome/browser/prerender/prerender_origin.cc
@@ -18,11 +18,13 @@ const char* kOriginNames[] = {
   "[Deprecated] Omnibox (conservative)",
   "[Deprecated] Omnibox (exact)",
   "Omnibox",
-  "Max"
+  "None",
+  "Max",
 };
 COMPILE_ASSERT(arraysize(kOriginNames) == ORIGIN_MAX + 1,
                PrerenderOrigin_name_count_mismatch);
-}
+
+}  // namespace
 
 const char* NameFromOrigin(Origin origin) {
   DCHECK(static_cast<int>(origin) >= 0 &&