Revert of Remove GetAttributes from the mix to avoid another virtual dispatch. (patchset #2 id:40001 of https://codereview.chromium.org/1175973002/)

Reason for revert:
It broke webkit_unit_tests

Original issue's description:
> Remove GetAttributes from the mix to avoid another virtual dispatch.
>
> BUG=chromium:495949,v8:4137
> LOG=n
>
> Committed: https://crrev.com/2269b8b5a696bf4eef13590093151bff624d4175
> Cr-Commit-Position: refs/heads/master@{#28953}

TBR=verwaest@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:495949,v8:4137

Review URL: https://codereview.chromium.org/1179933002

Cr-Commit-Position: refs/heads/master@{#28958}