[system_health] Reduce the number of article reads in globo story

The renderer OOMs on system_health.common benchmark on Android One
device because of tracing and other metrics being enabled. So, reduce
the number of article reads.

BUG=714650
R=nednguyen@google.com,perezju@chromium.org

Review-Url: https://codereview.chromium.org/2842593002
Cr-Commit-Position: refs/heads/master@{#466868}

tools/perf/page_sets/system_health/browsing_stories.py

@@ -565,7 +565,7 @@ class BrowseGloboMobileStory(_ArticleBrowsingStory):
   SUPPORTED_PLATFORMS = platforms.MOBILE_ONLY
   TAGS = [story_tags.EMERGING_MARKET]
 
-  ITEMS_TO_VISIT = 4
+  ITEMS_TO_VISIT = 3  # 4 links causes renderer OOM crbug.com/714650.
   ITEM_SELECTOR = '.hui-premium__title'
   COMPLETE_STATE_WAIT_TIMEOUT = 150