[Android] Don't wait for background tabs

tools/perf/measurements/session_restore.py

Index: tools/perf/measurements/session_restore.py
diff --git a/tools/perf/measurements/session_restore.py b/tools/perf/measurements/session_restore.py
index 5ad03a1065fe7d222aabeb4d68b23a4a722c314e..7adfe4a57ecb92b0f73e16c43492cbff368218c4 100644
--- a/tools/perf/measurements/session_restore.py
+++ b/tools/perf/measurements/session_restore.py
@@ -51,9 +51,17 @@ class SessionRestore(startup.Startup):
 
   def MeasurePage(self, page, tab, results):
     # Wait for all tabs to finish loading.
-    for i in xrange(len(tab.browser.tabs)):
-      t = tab.browser.tabs[i]
+    if 'android' in tab.browser.browser_type:

[tonyg, 2014/02/12 22:25:57]

I don't like defining the metric differently by platform. I think the metric
should just be Speed Index measured from launching the browser until foreground
tab visually complete.

If that is too much to bite off immediately, then I recommend we do the proposed
android behavior for all platforms.

[aberent, 2014/02/13 11:37:43]

Switched to Android behaviour in all cases. Switching to speed index looks more
difficult, since it depends on polling the tab to decide whether there is more
data coming, and in this case we want to start timing before the tab (or Chrome)
exists. As such I am not doing that now.

+      # On android the background tabs are loaded on demand, so wont have been
+      # loaded at this stage; so only wait for the foreground tab. Also
+      # document.hidden is broken on Android - crbug.com/322544 so assume this
+      # is tab[0]
+      t = tab.browser.tabs[0]
       t.WaitForDocumentReadyStateToBeComplete()
+    else:
+      for i in xrange(len(tab.browser.tabs)):
+        t = tab.browser.tabs[i]
+        t.WaitForDocumentReadyStateToBeComplete()
 
     # Record CPU usage from browser start to when all pages have loaded.
     self._cpu_metric.Stop(None, None)