Add chrome://site-engagement WebUI.

chrome/browser/engagement/site_engagement_service.h

Index: chrome/browser/engagement/site_engagement_service.h
diff --git a/chrome/browser/engagement/site_engagement_service.h b/chrome/browser/engagement/site_engagement_service.h
index 60644a4a4e3f504721d10a8a2e0666eb635dac34..2ab67a749a1cfe4fa1129eb7cc1aa233cac16b54 100644
--- a/chrome/browser/engagement/site_engagement_service.h
+++ b/chrome/browser/engagement/site_engagement_service.h
@@ -5,6 +5,8 @@
 #ifndef CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_SERVICE_H_
 #define CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_SERVICE_H_
 
+#include <map>
+
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/time/default_clock.h"
@@ -114,6 +116,9 @@ class SiteEngagementService : public KeyedService,
   explicit SiteEngagementService(Profile* profile);
   ~SiteEngagementService() override;
 
+  // Returns a map of all stored origins and their engagement scores.
+  std::map<GURL, int> GetScoreMap();
+
   // Update the karma score of the origin matching |url| for user navigation.
   void HandleNavigation(const GURL& url);