[Android] Don't wait for background tabs

tools/perf/metrics/startup_metric.py

Index: tools/perf/metrics/startup_metric.py
diff --git a/tools/perf/metrics/startup_metric.py b/tools/perf/metrics/startup_metric.py
index d0d400c4ce57cc61371d83e1dfc6d2374928a615..1e742ee74024c12ee5222a4453ff9fc046d8ef06 100644
--- a/tools/perf/metrics/startup_metric.py
+++ b/tools/perf/metrics/startup_metric.py
@@ -41,17 +41,15 @@ class StartupMetric(Metric):
       return None
     return (int(high_bytes) << 32) | (int(low_bytes) << 1)
 
-  # pylint: disable=W0101
   def _RecordTabLoadTimes(self, tab, browser_main_entry_time_ms, results):
     """Records the tab load times for the browser. """
     tab_load_times = []
     TabLoadTime = collections.namedtuple(
         'TabLoadTime',
-        ['load_start_ms', 'load_duration_ms', 'is_foreground_tab'])
-    num_open_tabs = len(tab.browser.tabs)
-    for i in xrange(num_open_tabs):
+        ['load_start_ms', 'load_duration_ms'])
+
+    def RecordTabLoadTime(t):
       try:
-        t = tab.browser.tabs[i]
         t.WaitForDocumentReadyStateToBeComplete()
 
         result = t.EvaluateJavaScript(
@@ -61,51 +59,34 @@ class StartupMetric(Metric):
         if 'load_start_ms' not in result or 'load_duration_ms' not in result:
           raise Exception("Outdated Chrome version, "
               "statsCollectionController.tabLoadTiming() not present")
-          return
         if result['load_duration_ms'] is None:
           tab_title = t.EvaluateJavaScript('document.title')
           print "Page: ", tab_title, " didn't finish loading."
-          continue
+          return
 
-        is_foreground_tab = t.EvaluateJavaScript('!document.hidden')
         tab_load_times.append(TabLoadTime(
             int(result['load_start_ms']),
-            int(result['load_duration_ms']),
-            is_foreground_tab))
+            int(result['load_duration_ms'])))
       except util.TimeoutException:
         # Low memory Android devices may not be able to load more than
         # one tab at a time, so may timeout when the test attempts to
         # access a background tab. Ignore these tabs.
-        logging.error("Tab number: %d timed out on JavaScript access" % i)
-        continue
-
-    # Postprocess results
-    load_complete_times = (
-        [t.load_start_ms + t.load_duration_ms for t in tab_load_times])
-    load_complete_times.sort()
-
-    if 'android' in tab.browser.browser_type:
-      # document.hidden is broken on Android - crbug.com/322544.
-      foreground_tab_stats = [tab_load_times[0]]
-    else:
-      foreground_tab_stats = (
-          [t for t in tab_load_times if t.is_foreground_tab == True])
-    if (len(foreground_tab_stats) != 1):
-      raise Exception ("More than one foreground tab? ", foreground_tab_stats)
-    foreground_tab_stats = foreground_tab_stats[0]
-
-    # Report load stats.
+        logging.error("Tab timed out on JavaScript access")
+
+    # Only measure the foreground tab. We can't measure all tabs on Android
+    # because on Android the data of the background tabs is loaded on demand,
+    # when the user switches to them, rather than during startup. In view of
+    # this, to get the same measures on all platform, we only measure the
+    # foreground tab on all platforms.
+
+    RecordTabLoadTime(tab.browser.foreground_tab)
+
+    foreground_tab_stats = tab_load_times[0]
     foreground_tab_load_complete = ((foreground_tab_stats.load_start_ms +
         foreground_tab_stats.load_duration_ms) - browser_main_entry_time_ms)
-
     results.Add(
         'foreground_tab_load_complete', 'ms', foreground_tab_load_complete)
 
-    if num_open_tabs > 1:
-      last_tab_load_complete = (
-          load_complete_times[-1] - browser_main_entry_time_ms)
-      results.Add('last_tab_load_complete', 'ms', last_tab_load_complete)
-
   def AddResults(self, tab, results):
     get_histogram_js = 'statsCollectionController.getBrowserHistogram("%s")'