HTMLTableElement.insertRow()'s argument default value should be -1

HTMLTableElement.insertRow()'s argument default value should be -1, not
0, as per the specification:
http://www.whatwg.org/specs/web-apps/current-work/multipage/tabular-data.html#htmltableelement

The new behavior matches the one of Firefox 29 and IE11.

R=arv@chromium.org, tkent@chromium.org
TEST=fast/dom/HTMLTableElement/insertRow-default-argument.html
BUG=369803

Review URL: https://codereview.chromium.org/270213007

git-svn-id: svn://svn.chromium.org/blink/trunk@173578 bbb929c8-8fbe-4397-9dbb-9b2b20218538