Fix parsing of 'start' attribute of <ol> element

Fix parsing of 'start' attribute of <ol> element
by using parseHTMLInteger instead of toInt.

This also fixes the last remaining
reflection-grouping.html failures.

BUG=651762, 634796

Review-Url: https://codereview.chromium.org/2493533002
Cr-Commit-Position: refs/heads/master@{#431495}
2 files changed