Add new prerender origin type for <link rel=next ...> launched prerenders.

chrome/browser/prerender/prerender_histograms.cc

Index: chrome/browser/prerender/prerender_histograms.cc
diff --git a/chrome/browser/prerender/prerender_histograms.cc b/chrome/browser/prerender/prerender_histograms.cc
index e83509349a5f70279cb3827871e46b2dceab7087..11d63bcedf7661521dccdf557a515369a3704812 100644
--- a/chrome/browser/prerender/prerender_histograms.cc
+++ b/chrome/browser/prerender/prerender_histograms.cc
@@ -62,6 +62,8 @@ std::string GetHistogramName(Origin origin, uint8 experiment_id,
         return ComposeHistogramName("externalrequest", name);
     case ORIGIN_INSTANT:
       return ComposeHistogramName("Instant", name);
+    case ORIGIN_LINK_REL_NEXT:
+      return ComposeHistogramName("webnext", name);
     case ORIGIN_GWS_PRERENDER:  // Handled above.
     default:
       NOTREACHED();
@@ -125,6 +127,8 @@ bool OriginIsOmnibox(Origin origin) {
     HISTOGRAM; \
   } else if (origin == ORIGIN_INSTANT) { \
     HISTOGRAM; \
+  } else if (origin == ORIGIN_LINK_REL_NEXT) { \
+    HISTOGRAM; \
   } else if (experiment != kNoExperiment) { \
     HISTOGRAM; \
   } else { \