Add a fallback to creation date for Recent bookmarks on NTP

components/ntp_snippets/bookmarks/bookmark_last_visit_utils.h

Index: components/ntp_snippets/bookmarks/bookmark_last_visit_utils.h
diff --git a/components/ntp_snippets/bookmarks/bookmark_last_visit_utils.h b/components/ntp_snippets/bookmarks/bookmark_last_visit_utils.h
index 01fd935e791f3880452f99c9f89f2811e87d2b0a..9ef2c23ad8bbd27dce53270d70f979d8e91c0b4b 100644
--- a/components/ntp_snippets/bookmarks/bookmark_last_visit_utils.h
+++ b/components/ntp_snippets/bookmarks/bookmark_last_visit_utils.h
@@ -28,13 +28,18 @@ void UpdateBookmarkOnURLVisitedInMainFrame(
     const GURL& url);
 
 // Gets the last visit date for a given bookmark |node|. The visit when the
-// bookmark is created also counts.
-base::Time GetLastVisitDateForBookmark(const bookmarks::BookmarkNode* node);
+// bookmark is created also counts. If |use_creation_date| is true, creation
+// date of the bookmark is considered instead of its last visit date (useful for
+// the transition phase M53 -> M54 when no last visit data is available).

[Marc Treib, 2016/08/17 11:29:05]

Hm, so even in the "fallback mode", wouldn't we still want to use the visit date
if we have it? So that users gracefully graduate out of that mode?

And I guess we don't want to use the creation date in the regular mode because
it can be the date when the bookmark was synced? I.e. on a new device, all
bookmarks will have a creation date of "now"?
That seems super unfortunate... can we maybe detect that case? Does the bookmark
have some "from sync" tag?

+base::Time GetLastVisitDateForBookmark(const bookmarks::BookmarkNode* node,
+                                       bool use_creation_date);
 
 // Like GetLastVisitDateForBookmark, but it returns the unix epoch if the
-// bookmark is dismissed from NTP.
+// bookmark is dismissed from NTP. If |use_creation_date| is true, creation
+// date of the bookmark is considered instead of its last visit date (useful for
+// the transition phase M53 -> M54 when no last visit data is available).
 base::Time GetLastVisitDateForBookmarkIfNotDismissed(
-    const bookmarks::BookmarkNode* node);
+    const bookmarks::BookmarkNode* node, bool use_creation_date);
 
 // Marks all bookmarks with the given URL as dismissed.
 void MarkBookmarksDismissed(bookmarks::BookmarkModel* bookmark_model,
@@ -46,13 +51,19 @@ bool IsDismissedFromNTPForBookmark(const bookmarks::BookmarkNode* node);
 // Removes the dismissed flag from all bookmarks (only for debugging).
 void MarkAllBookmarksUndismissed(bookmarks::BookmarkModel* bookmark_model);
 
+// Returns true if and only if there is at least one bookmark in
+// |bookmark_model| that has information about its last visit associated.
+bool IsLastVisitDataAvailable(bookmarks::BookmarkModel* bookmark_model);
+
 // Returns the list of most recently visited, non-dismissed bookmarks.
 // For each bookmarked URL, it returns the most recently created bookmark.
 // The result is ordered by visit time (the most recent first). Only bookmarks
 // visited after |min_visit_time| are considered, at most |max_count| bookmarks
-// are returned.
+// are returned. If |use_creation_date| is true, the creation date of a bookmark
+// is used instead of the last visit date.
 std::vector<const bookmarks::BookmarkNode*> GetRecentlyVisitedBookmarks(
     bookmarks::BookmarkModel* bookmark_model,
+    bool use_creation_date,
     int max_count,
     const base::Time& min_visit_time);