Gardening: Many of focus-by-mouse tests are not flaky now.

BUG=254332
TBR=keishi@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/34233002

git-svn-id: svn://svn.chromium.org/blink/trunk@160124 bbb929c8-8fbe-4397-9dbb-9b2b20218538