Modify list_system_health_stories to generate_system_health_csv

tools/perf/page_sets/system_health/long_running_stories.py

Index: tools/perf/page_sets/system_health/long_running_stories.py
diff --git a/tools/perf/page_sets/system_health/long_running_stories.py b/tools/perf/page_sets/system_health/long_running_stories.py
index a32ea451042d077a37e124b23dc57a1a60f27e13..c4fba0a9f19b6dba18c39f0e361aa40156f43f2b 100644
--- a/tools/perf/page_sets/system_health/long_running_stories.py
+++ b/tools/perf/page_sets/system_health/long_running_stories.py
@@ -30,6 +30,15 @@ class _LongRunningStory(system_health_story.SystemHealthStory):
       if self._take_memory_measurement:
         action_runner.MeasureMemory()
 
+  @classmethod
+  def GenerateStoryDescription(cls):
+    if cls.BACKGROUND:
+      return ('Load %s then open a new blank tab and let the loaded page stay '
+              'in background for %s seconds.' % (cls.URL, IDLE_TIME_IN_SECONDS))
+    else:
+      return ('Load %s then let it stay in foreground for %s seconds.' %
+              (cls.URL, IDLE_TIME_IN_SECONDS))
+
 
 ##############################################################################
 # Long running Gmail stories.