Gardening: test expectations update

Mark two flaky tests:
fast/scrolling/hover-during-scroll.html
http/tests/security/contentSecurityPolicy/1.1/frame-ancestors/frame-ancestors-nested-same-in-same-none-block.html

BUG=353751,353754
TEST=
TBR=zmo@chromium.org

Review URL: https://codereview.chromium.org/201153017

git-svn-id: svn://svn.chromium.org/blink/trunk@169485 bbb929c8-8fbe-4397-9dbb-9b2b20218538