Fix tab_switching to support flag --pageset-repeat properly

tools/perf/page_sets/system_health/multi_tab_stories.py

Index: tools/perf/page_sets/system_health/multi_tab_stories.py
diff --git a/tools/perf/page_sets/system_health/multi_tab_stories.py b/tools/perf/page_sets/system_health/multi_tab_stories.py
index a9ab0c741024d2fa37508cdd7157ea010c4e384d..5583ad63f1c8ba70b67dbd142a4946a5b155ff77 100644
--- a/tools/perf/page_sets/system_health/multi_tab_stories.py
+++ b/tools/perf/page_sets/system_health/multi_tab_stories.py
@@ -15,16 +15,26 @@ from telemetry import benchmark
 class MultiTabStory(system_health_story.SystemHealthStory):
   ABSTRACT_STORY = True
 
+  def __init__(self, story_set, take_memory_measurement):
+    super(MultiTabStory, self).__init__(story_set, take_memory_measurement)
+    self._pageset_repeat = 1
+
+  def Run(self, shared_state):
+    finder_options = getattr(shared_state, '_finder_options')
+    self._pageset_repeat = finder_options.pageset_repeat
+    super(MultiTabStory, self).Run(shared_state)
+
   def RunNavigateSteps(self, action_runner):
     tabs = action_runner.tab.browser.tabs
 
-    # No need to create the first tab as there is already one
-    # when the browser is ready,
-    if self.URL_LIST:
-      action_runner.Navigate(self.URL_LIST[0])
-    for url in self.URL_LIST[1:]:
-      new_tab = tabs.New()
-      new_tab.action_runner.Navigate(url)
+    # If this is the first pageset, don't have to create the first tab
+    # as there is already one when the browser is ready,
+    for i, url in enumerate(self.URL_LIST):
+      if i == 0 and len(action_runner.tab.browser.tabs) == 1:
+        action_runner.Navigate(url)
+      else:
+        new_tab = tabs.New()
+        new_tab.action_runner.Navigate(url)
 
     for i, url in enumerate(self.URL_LIST):
       try:
@@ -34,6 +44,13 @@ class MultiTabStory(system_health_story.SystemHealthStory):
                         % (i, url))
 
   def RunPageInteractions(self, action_runner):
+    # if tab switching on every pageset, the metrics data would be a mix of
+    # tab switching on different tab counts and is hard to analyze. only
+    # tab switching on the last pageset
+    if self._pageset_repeat != 1 and len(action_runner.tab.browser.tabs) != \
+        len(self.URL_LIST) * self._pageset_repeat:
+      return
+
     for tab in action_runner.tab.browser.tabs:
       tab.Activate()
       tab.WaitForFrameToBeDisplayed()