Revert of Revert of Remove GetAttributes from the mix to avoid another virtual dispatch. (patchset #1 id:1 of https://codereview.chromium.org/1179933002/)

Reason for revert:
Reland, this didn't break anything.

Original issue's description:
> 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
>
> Committed: https://crrev.com/ae639d2ad646237e2f413259a0f116845ef96440
> Cr-Commit-Position: refs/heads/master@{#28958}

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

Review URL: https://codereview.chromium.org/1182603002

Cr-Commit-Position: refs/heads/master@{#28966}