Revert of Remove the assertion that number of expected tabs must equal to number of live tabs temporarily.

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

Index: tools/telemetry/telemetry/core/backends/chrome/tab_list_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/tab_list_backend.py b/tools/telemetry/telemetry/core/backends/chrome/tab_list_backend.py
index 80e852fec55ab9b1615ec7f067a14baa39c298d3..95854c36057d6af8a293ecff6d3435d1fecf384f 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/tab_list_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/tab_list_backend.py
@@ -2,7 +2,6 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import logging
 import urllib2
 
 from telemetry.core import exceptions
@@ -68,16 +67,7 @@
           'Number of opening tabs is %i, whereas number of live tabs is %i, '
           'Tried to get tab at index %i but this may not return the right tab.'
           % (self._num_expected_tabs, len(self), index))
-    # TODO(nednguyen): fix this by adding wait in DidStartBrowser to make sure
-    # that all the tabs have been loaded.
-    if self._num_expected_tabs != len(self):
-      logging.warning(
-          'Number of expected tabs was not intialized correctly (Num expected '
-          'tabs is %i, whereas number of live tabs is %i). This is probably due'
-          ' to the browser did not wait long enough for all tabs to be loaded '
-          ' before intializing number of expected tabs.' %
-          (self._num_expected_tabs, len(self)))
-      self._num_expected_tabs = len(self)
+    assert self._num_expected_tabs == len(self)
 
     return super(TabListBackend, self).__getitem__(index)