Add instrumentation to see how often a local predictor prerender could be

chrome/browser/prerender/prerender_local_predictor.h

Index: chrome/browser/prerender/prerender_local_predictor.h
===================================================================
--- chrome/browser/prerender/prerender_local_predictor.h	(revision 199567)
+++ chrome/browser/prerender/prerender_local_predictor.h	(working copy)
@@ -18,6 +18,7 @@
 
 namespace content {
 class SessionStorageNamespace;
+class WebContents;
 }
 
 namespace gfx {
@@ -84,6 +85,10 @@
     EVENT_ISSUING_PRERENDER = 43,
     EVENT_NO_PRERENDER_CANDIDATES = 44,
     EVENT_GOT_HISTORY_ISSUING_LOOKUP = 45,
+    EVENT_TAB_HELPER_URL_SEEN = 46,
+    EVENT_TAB_HELPER_URL_SEEN_MATCH = 47,
+    EVENT_TAB_HELPER_URL_SEEN_NAMESPACE_MATCH = 48,
+    EVENT_PRERENDER_URL_LOOKUP_MULTIPLE_SOURCE_WEBCONTENTS_FOUND = 49,
     EVENT_MAX_VALUE
   };
 
@@ -103,6 +108,8 @@
 
   void OnPLTEventForURL(const GURL& url, base::TimeDelta page_load_time);
 
+  void OnTabHelperURLSeen(const GURL& url, content::WebContents* web_contents);
+
  private:
   struct PrerenderProperties;
   HistoryService* GetHistoryIfExists() const;
@@ -155,6 +162,12 @@
 
   base::WeakPtrFactory<PrerenderLocalPredictor> weak_factory_;
 
+  // Indicates whether the current prerender represented by prerender_handle_
+  // matched a load in some tab contents, to shed light on how many prerenders
+  // that could have possibily been swapped in were not swapped in. For
+  // measurement purposes only.
+  bool current_prerender_would_have_matched_;
+
   DISALLOW_COPY_AND_ASSIGN(PrerenderLocalPredictor);
 };