Telemetry: Fix facebook.com on key_mobile_sites.

tools/perf/page_sets/key_mobile_sites.json

 {
   "description": "Key mobile sites",
   "archive_data_file": "../data/key_mobile_sites.json",
   "credentials_path": "../data/credentials.json",
   "user_agent_type": "mobile",
   "smoothness": { "action": "scroll" },
   "pages": [
     {
       "url": "http://www.androidpolice.com/2012/10/03/rumor-evidence-mounts-that-an-lg-optimus-g-nexus-is-coming-along-with-a-nexus-phone-certification-program/",
       "why": "crbug.com/242544"
@@ skipping 52 matching lines @@
       "smoothness": {
         "action": "scroll",
         "scroll_is_infinite": true
       }
     },
     {
       "url": "https://facebook.com/barackobama",
       "why": "#1 (Alexa global)",
       "navigate_steps": [
         { "action": "navigate" },
-        { "action": "wait", "javascript": "document.getElementById('u_0_c') !== null" }
+        { "action": "wait", "javascript": "document.getElementById('u_0_c') !== null && document.body.scrollHeight > window.innerHeight" }

[tonyg, 2013/09/04 17:27:19]

Does this work for all screen sizes? I'm worried that it might only work on
smaller screens.

[Dominik Grewe, 2013/09/04 20:05:52]

It should work if there's anything to scroll :) An alternative would be to wait
for a second or so to make sure the values have been updated.

[tonyg, 2013/09/04 20:29:43]

You are right. The test will fail anyway if there is nothing to scroll.

       ]
     },
     {
       "url": "http://m.youtube.com/watch?v=9hBpF_Zj4OA",
       "why": "#3 (Alexa global)",
       "navigate_steps": [
         { "action": "navigate"},
         { "action": "wait", "javascript": "document.getElementById('paginatortarget') !== null"}
       ]
     },
@@ skipping 141 matching lines @@
         "remaining_scroll_distance_function": "function() { return Math.max(0, 1250 + document.getElementById('element-19').contentDocument.getElementById('element-22').getBoundingClientRect().top); }"
       }
     },
     {
       "disabled": "Doesn't scroll; crbug.com/249736",
       "url": "http://forecast.io",
       "why": "crbug.com/231413"
     }
   ]
 }