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

chrome/browser/prerender/prerender_manager.h

Index: chrome/browser/prerender/prerender_manager.h
===================================================================
--- chrome/browser/prerender/prerender_manager.h	(revision 199567)
+++ chrome/browser/prerender/prerender_manager.h	(working copy)
@@ -310,6 +310,10 @@
     return logged_in_predictor_table_;
   }
 
+  PrerenderLocalPredictor* local_predictor() {
+    return local_predictor_.get();
+  }
+
  protected:
   class PrerenderData : public base::SupportsWeakPtr<PrerenderData> {
    public: