Gracefully handle <meta http-equiv name content> elements.

If presented with a <meta> element having both a 'name' and
'http-equiv' attribute, try interpreting the 'name' attribute first
before _also_ considering 'http-equiv'. The specification requires
that at most one of these attributes to be used, but authors don't
always keep their side of the bargain.

This simply reinstates previous behavior, something that regressed in
https://codereview.chromium.org/25728006/ (it ignores 'http-equiv' if
'name' is supplied, even if the latter is set to some unknown value.)

R=
BUG=332090

Review URL: https://codereview.chromium.org/126313002

git-svn-id: svn://svn.chromium.org/blink/trunk@164642 bbb929c8-8fbe-4397-9dbb-9b2b20218538