Bring back fast paths for HTMLTagCollection / ClassCollection's access

Bring back fast paths for HTMLTagCollection / ClassCollection's access.
Those were removed in r166263, when switching them from LiveNodeList to
HTMLCollection type. r166263 caused Dromaeo's dom-query test to regress by
~12% according to our build bots and this CL is an attempt to address the
issue. Locally, I see a 3-4% improvement on dom-query but I am hoping the
bots get better results.

R=arv, haraken, adamk
BUG=340325

Review URL: https://codereview.chromium.org/138653004

git-svn-id: svn://svn.chromium.org/blink/trunk@166427 bbb929c8-8fbe-4397-9dbb-9b2b20218538