Gardening: Mark textfieldselection/selection as slow/failing
Gardening: Mark textfieldselection/selection as slow/failing

This appears to have been failing on debug bots since it was
committed.

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=imported%2Fweb-platform-tests%2Fhtml%2Fsemantics%2Fforms%2Ftextfieldselection%2Fselection.html&testType=layout-tests

NOTRY=true
TBR=tkent@chromium.org,dstockwell@chromium.org
BUG=490511

Review URL: https://codereview.chromium.org/1167323002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@196699 bbb929c8-8fbe-4397-9dbb-9b2b20218538

Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk