ensure 'no browsing context' test in clear.py isn't relying on the pr…

…evious page runs

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1499135
gecko-commit: 97be1d70d0cd4637a4bd02e984d179b3f1a600e8
gecko-integration-branch: mozilla-inbound
gecko-reviewers: ato

webdriver/tests/element_clear/clear.py

@@ -1,6 +1,7 @@
 # META: timeout=long
 
 import pytest
+import time
 
 from webdriver import Element
 
@@ -47,7 +48,7 @@ def test_null_response_value(session):
 
 
 def test_no_browsing_context(session, closed_window):
-    element = Element("foo", session)
+    element = Element("foo" + str(time.time()), session)
 
     response = element_clear(session, element)
     assert_error(response, "no such window")