Mark storage/indexeddb/createIndex-deleteObjectStore.htm as flaky

BUG=374230
TBR=jsbell@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/289973005

git-svn-id: svn://svn.chromium.org/blink/trunk@174240 bbb929c8-8fbe-4397-9dbb-9b2b20218538