Implement important sites dialog for desktop.

chrome/browser/engagement/important_sites_util.h

Index: chrome/browser/engagement/important_sites_util.h
diff --git a/chrome/browser/engagement/important_sites_util.h b/chrome/browser/engagement/important_sites_util.h
index 408dff05d7c3f92d8115c2b426b2f2caca2629b0..364da285f30c9036214524bce3d0bdab493af516 100644
--- a/chrome/browser/engagement/important_sites_util.h
+++ b/chrome/browser/engagement/important_sites_util.h
@@ -26,6 +26,16 @@ class ImportantSitesUtil {
     int32_t reason_bitfield = 0;
   };
 
+  // Do not change the values here, as they are used for UMA histograms.

[dschuyler, 2017/04/07 00:02:05]

The comment is clear, but can it be extended to point the next coder to where
the a change/addition could be made properly? Maybe a "See: ....." line here?

[dullweber, 2017/04/07 09:39:21]

I just moved this enum from the .cc to the header to make it accessible to other
classes. I guess that new values could be appended but I have to ask Daniel
about this first.

+  enum ImportantReason {
+    ENGAGEMENT = 0,
+    DURABLE = 1,
+    BOOKMARKS = 2,
+    HOME_SCREEN = 3,
+    NOTIFICATIONS = 4,
+    REASON_BOUNDARY
+  };
+
   static bool IsDialogDisabled(Profile* profile);
 
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);