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

Review URL: https://codereview.chromium.org/766703002

Cr-Commit-Position: refs/heads/master@{#25541}
Switch backedge table in scheduler to use ZoneVector.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/761733002

Cr-Commit-Position: refs/heads/master@{#25542}
Start immediate dominator propagation at entry to floating control.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/761673004

Cr-Commit-Position: refs/heads/master@{#25543}
Just finalize incremental marking when marking is done in idle notification.

BUG=

Review URL: https://codereview.chromium.org/733893003

Cr-Commit-Position: refs/heads/master@{#25544}
Re-land: Distinguish beween final incremental mark-compact and full mark-compact event in IdleNotification.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/765743002

Cr-Commit-Position: refs/heads/master@{#25545}