Gardening: http/tests/security/contentSecurityPolicy/1.1/frame-ancestors/frame-ancestors-nested-same-in-same-url-block.html flaky

BUG=353763
TEST=
TBR=zmo@chromium.org

Review URL: https://codereview.chromium.org/203293008

git-svn-id: svn://svn.chromium.org/blink/trunk@169489 bbb929c8-8fbe-4397-9dbb-9b2b20218538