Skip 'accessibilityController' property in the cached properties test

https://codereview.chromium.org/172263002/ moves AccessibilityController
from CppBoundClass to gin::Wrappable, and that CL changes this cached-
properties test's result so that 'accessibilityController' is enumerated
as properties of an object. However, it is hard to expect a stable cache
result of WebAXObject of AccessibilityController for now.

BUG=297480, 331301, 347331

Review URL: https://codereview.chromium.org/184233004

git-svn-id: svn://svn.chromium.org/blink/trunk@168564 bbb929c8-8fbe-4397-9dbb-9b2b20218538