X87: Use weak cells to embed maps in store handler.

port 3fc9c9b665baaa434c672efcbff632a2eae86f56

original commit message:

  Use weak cells to embed maps in store handler.
  BUG=v8:3629
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/779843002

Cr-Commit-Position: refs/heads/master@{#25649}