1) CSA::StoreMap() added which triggers map-specific write barrier
   unlike StoreObjectField() which triggers the full write barrier.
2) CSA::StoreMapNoWriteBarrier(object, map_root_index) added.
3) StoreMapNoWriteBarrier() is used for storing immortal immovable
   maps since they don't require write barriers even for objects in
   old space.

BUG=

Review-Url: https://codereview.chromium.org/2544793002
Cr-Commit-Position: refs/heads/master@{#41435}