port 1e277012 (r31914)

   original commit message:
   Avoid write barriers when storing values in the root set, and use
   cheaper write barriers for storing maps or tagged pointers. Also
   improve the generated code for write barriers, utilizing the out
   of line code mechanism that is available to TurboFan backends,
   which moves the unlikely case out of the hot path.

BUG=

Review URL: https://codereview.chromium.org/1435743003

Cr-Commit-Position: refs/heads/master@{#31935}