[Telemetry] Add comment to page_set_smoke_test. Noop change

tools/telemetry/telemetry/unittest_util/page_set_smoke_test.py

Index: tools/telemetry/telemetry/unittest_util/page_set_smoke_test.py
diff --git a/tools/telemetry/telemetry/unittest_util/page_set_smoke_test.py b/tools/telemetry/telemetry/unittest_util/page_set_smoke_test.py
index bf63d94370516d4de4f59909fe9d365b39a14725..7d89b98b138570ae3b51797084345e36043efd51 100644
--- a/tools/telemetry/telemetry/unittest_util/page_set_smoke_test.py
+++ b/tools/telemetry/telemetry/unittest_util/page_set_smoke_test.py
@@ -103,6 +103,8 @@ class PageSetSmokeTest(unittest.TestCase):
   def CheckAttributesOfPageBasicAttributes(self, page):
     self.assertTrue(not hasattr(page, 'disabled'))
     self.assertTrue(
+       # We use basestring instead of str because page's url can be string of
+       # unicode.
        isinstance(page.url, basestring),
        msg='page %s \'s url must have type string' % page.display_name)
     self.assertTrue(