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

Bug: 878390
Change-Id: I51d46f052b632183c18581ce27a82f84dc832805
Reviewed-on: https://chromium-review.googlesource.com/c/1261438Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596741}

tools/perf/page_sets/data/system_health_desktop.json

@@ -30,6 +30,9 @@
         "browse:news:hackernews": {
             "DEFAULT": "system_health_desktop_014.wprgo"
         },
+        "browse:news:hackernews:2018": {
+            "DEFAULT": "system_health_desktop_45995e1b9c.wprgo"
+        },
         "browse:news:nytimes": {
             "DEFAULT": "system_health_desktop_015.wprgo"
         },

tools/perf/page_sets/data/system_health_desktop_45995e1b9c.wprgo.sha1

+45995e1b9c80dd850a1310aab899da9e9127e5d7
\ No newline at end of file

tools/perf/page_sets/system_health/browsing_stories.py

@@ -186,6 +186,14 @@ class HackerNewsDesktopStory(_ArticleBrowsingStory):
   TAGS = [story_tags.YEAR_2016]
 
 
+class HackerNewsDesktopStory2018(_ArticleBrowsingStory):
+  NAME = 'browse:news:hackernews:2018'
+  URL = 'https://news.ycombinator.com'
+  ITEM_SELECTOR = '.athing .title > a'
+  SUPPORTED_PLATFORMS = platforms.DESKTOP_ONLY
+  TAGS = [story_tags.YEAR_2018]
+
+
 class NytimesDesktopStory(_ArticleBrowsingStory):
   """The third top website in http://www.alexa.com/topsites/category/News"""
   NAME = 'browse:news:nytimes'