Add an isolate file for webkit_unit_tests on Android.

BUG=263019
TEST=webkit_unit_tests
R=abarth@chromium.org, maruel@chromium.org

Review URL: https://codereview.chromium.org/19719003

git-svn-id: svn://svn.chromium.org/blink/trunk@154686 bbb929c8-8fbe-4397-9dbb-9b2b20218538