Predeclare globals required by the test framework to avoid walking the prototype chain.

Otherwise http/tests/security/xss-DENIED-method-with-iframe-proto.html double-faults while trying to read those global variables that aren't declared.

BUG=

Review URL: https://codereview.chromium.org/405893003

git-svn-id: svn://svn.chromium.org/blink/trunk@178553 bbb929c8-8fbe-4397-9dbb-9b2b20218538