Also wait for gaia document.readyState to be complete.

BUG=361862
TEST=power_LoadTest
NOTRY=True

Review URL: https://codereview.chromium.org/302003005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@273880 0039d316-1c4b-4281-b951-d872f2087c98

tools/telemetry/telemetry/core/backends/chrome/oobe.py

@@ -16,7 +16,9 @@ class Oobe(web_contents.WebContents):
     for gaia_context in range(15):
       try:
         if self.EvaluateJavaScriptInContext(
-            "document.getElementById('Email') != null", gaia_context):
+            "document.readyState == 'complete' && "
+            "document.getElementById('Email') != null",
+            gaia_context):
           return gaia_context
       except exceptions.EvaluateException:
         pass