[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..ccd39c1e4430ac1beb13fa133ad80cc8476a5c77 100644
--- a/tools/perf/metrics/startup_metric.py
+++ b/tools/perf/metrics/startup_metric.py
@@ -41,17 +41,16 @@ class StartupMetric(Metric):
       return None
     return (int(high_bytes) << 32) | (int(low_bytes) << 1)
 
-  # pylint: disable=W0101
+# 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):
+
+    def RecordTabLoadTime(t):
       try:
-        t = tab.browser.tabs[i]
         t.WaitForDocumentReadyStateToBeComplete()
 
         result = t.EvaluateJavaScript(
@@ -61,11 +60,10 @@ 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           raise Exception("Outdated Chrome version, "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(
@@ -76,35 +74,46 @@ class StartupMetric(Metric):
         # 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()
+        logging.error("Tab number: %d timed out on JavaScript access" % 0)
 
     if 'android' in tab.browser.browser_type:
-      # document.hidden is broken on Android - crbug.com/322544.
-      foreground_tab_stats = [tab_load_times[0]]
+      # On android the background tabs are loaded on demand, so wont have been
+      # loaded at this stage; only record the foreground tab. Also
+      # document.hidden is broken on Android - crbug.com/322544 so assume this
+      # is tab[0]

[jeremy, 2014/02/13 09:40:15]

Can you stick in a comment explaining in detail the Android behavior and that
we're doing the same thing on all platforms so we get the same measurement on
all of them.

+      RecordTabLoadTime(tab.browser.tabs[0])
+
+      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)
     else:
+      num_open_tabs = len(tab.browser.tabs)
+      for i in xrange(num_open_tabs):
+        RecordTabLoadTime(tab.browser.tabs[i])
+      # Postprocess results
+      load_complete_times = (
+          [t.load_start_ms + t.load_duration_ms for t in tab_load_times])
+      load_complete_times.sort()
+
       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]
+      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.
-    foreground_tab_load_complete = ((foreground_tab_stats.load_start_ms +
-        foreground_tab_stats.load_duration_ms) - browser_main_entry_time_ms)
+      # Report load stats.
+      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)
+      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)
+      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")'