DATALIST element: Filter DATALIST OPTIONs by sustring matching

Both of Firefox and Edge shows OPTIONs filtered by substring matching.  We
follow them.

It seems that Firefox shows OPTIONs with matched labels, and Edge shows OPTIONs
with matches values. We show OPTIONs with matched labels or values.

BUG=153991

Review-Url: https://codereview.chromium.org/2183773003
Cr-Commit-Position: refs/heads/master@{#407738}
2 files changed