Prevent crash in createInstanceTimesFromSyncbase

This patch prevents a crash in createInstanceTimesFromSyncbase where
a non-finite time would assert. This case is valid and we've added a test
to prove it.

This patch is a merge of http://trac.webkit.org/changeset/162459 by
Tamas Gergely <tgergely.u-szeged@partner.samsung.com>.

BUG=231531
NOTRY=true

Review URL: https://codereview.chromium.org/144333002

git-svn-id: svn://svn.chromium.org/blink/trunk@165498 bbb929c8-8fbe-4397-9dbb-9b2b20218538