MIPS: harmony-scoping: make assignment to 'const' a late error.

MIPS: harmony-scoping: make assignment to 'const' a late error.

Port 6ac4de87a8b01500b066a3e401e921d2d84b42db

Original commit message:
Per TC39 Nov 2014 decision.

This patch also changes behavior for "legacy const": assignments to sloppy const in strict mode is now also a type error. This fixes v8:2243 and also brings us in compliance with other engines re assignment to function names (see updated webkit test), but might have bigger implications.
That change can easily be reverted by changing Variable::IsSignallingAssignmentToConst.

BUG=v8:3713, v8:2243
LOG=N

[balazs.kilvady, 2014-11-27 10:07:52]

balazs.kilvady@imgtec.com changed reviewers:
+ akos.palfi@imgtec.com, danno@chromium.org, dslomov@chromium.org,
dusan.milosavljevic@imgtec.com, gergely.kis@imgtec.com, paul.lind@imgtec.com

[dusmil.imgtec, 2014-11-27 10:50:49]

LGTM.

[balazs.kilvady, 2014-11-27 10:51:17]

The CQ bit was checked by balazs.kilvady@imgtec.com

[commit-bot: I haz the power, 2014-11-27 10:51:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/766703002/1

[commit-bot: I haz the power, 2014-11-27 11:21:05]

Committed patchset #1 (id:1)

[Dmitry Lomov (no reviews), 2014-11-27 11:31:34]

lgtm