Thumbnails: Add some perf UMA

chrome/browser/thumbnails/thumbnail_tab_helper.h

Index: chrome/browser/thumbnails/thumbnail_tab_helper.h
diff --git a/chrome/browser/thumbnails/thumbnail_tab_helper.h b/chrome/browser/thumbnails/thumbnail_tab_helper.h
index b91b05ab115336cee6b24b0ac2744fd9874b0f84..1ea55e686e535e7ff9ad9ed0d92ff341024ef921 100644
--- a/chrome/browser/thumbnails/thumbnail_tab_helper.h
+++ b/chrome/browser/thumbnails/thumbnail_tab_helper.h
@@ -7,6 +7,7 @@
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/time/time.h"
 #include "chrome/browser/thumbnails/thumbnailing_context.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
@@ -71,10 +72,14 @@ class ThumbnailTabHelper
   const bool capture_on_load_finished_;
 
   content::NotificationRegistrar registrar_;
-  scoped_refptr<thumbnails::ThumbnailingContext> thumbnailing_context_;
 
   bool load_interrupted_;
 
+  scoped_refptr<thumbnails::ThumbnailingContext> thumbnailing_context_;
+
+  base::TimeTicks copy_from_surface_start_time_;
+  base::TimeTicks process_bitmap_start_time_;
+
   base::WeakPtrFactory<ThumbnailTabHelper> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ThumbnailTabHelper);