Bug 1410891 - Fix prompt handle assertions. r=maja_zf

The first assertion was never run because it was passed a tuple
of a response value and a boolean.  It now compares the response
value to the boolean using "is".

The second assertion mistakenly used the "==" (equals) operator
but should use "is" to get a better pytest error message.

MozReview-Commit-ID: HCCr5rExIYu

--HG--
extra : rebase_source : b6e087de9ab7041411e363bdbc4f5d1a7b0eb373

testing/web-platform/tests/webdriver/tests/element_retrieval/get_active_element.py

@@ -103,7 +103,7 @@ def test_handle_prompt_accept(new_session):
 
     assert_is_active_element(session, response)
     assert_dialog_handled(session, "accept #2")
-    assert read_global(session, "accept2"), True
+    assert read_global(session, "accept2") is True
 
     create_dialog(session)("prompt", text="accept #3", result_var="accept3")
 
@@ -142,7 +142,7 @@ def test_handle_prompt_missing_value(session, create_dialog):
 
     assert_error(response, "unexpected alert open")
     assert_dialog_handled(session, "dismiss #2")
-    assert session.execute_script("return dismiss2;") == False
+    assert session.execute_script("return dismiss2") is False
 
     create_dialog("prompt", text="dismiss #3", result_var="dismiss3")