[perf] Add browse:news:flipboard:2018 system health story

Bug: 878390
Change-Id: I6ba0ce622392c38fe1f7fc23fcfde7829bbe0480
Reviewed-on: https://chromium-review.googlesource.com/c/1261556Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597077}

tools/perf/page_sets/data/system_health_desktop.json

@@ -27,6 +27,9 @@
         "browse:news:flipboard": {
             "DEFAULT": "system_health_desktop_021.wprgo"
         },
+        "browse:news:flipboard:2018": {
+            "DEFAULT": "system_health_desktop_4c82ac641b.wprgo"
+        },
         "browse:news:hackernews": {
             "DEFAULT": "system_health_desktop_014.wprgo"
         },

tools/perf/page_sets/data/system_health_desktop_4c82ac641b.wprgo.sha1

+4c82ac641b02b0a49a57c608bf03fd98cecb5866
\ No newline at end of file

tools/perf/page_sets/system_health/browsing_stories.py

@@ -178,6 +178,15 @@ class FlipboardDesktopStory(_ArticleBrowsingStory):
   TAGS = [story_tags.YEAR_2016]
 
 
+class FlipboardDesktopStory2018(_ArticleBrowsingStory):
+  NAME = 'browse:news:flipboard:2018'
+  URL = 'https://flipboard.com/explore'
+  IS_SINGLE_PAGE_APP = True
+  ITEM_SELECTOR = '.cover-image'
+  SUPPORTED_PLATFORMS = platforms.DESKTOP_ONLY
+  TAGS = [story_tags.YEAR_2018]
+
+
 class HackerNewsDesktopStory(_ArticleBrowsingStory):
   NAME = 'browse:news:hackernews'
   URL = 'https://news.ycombinator.com'