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}
Fix Promise.resolve/Promise.reject unnecessarily scheduling a microtask.

R=rossberg@chromium.org, yangguo@chromium.org, adamk@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/777703002

Cr-Commit-Position: refs/heads/master@{#25650}
Fix path construction in perf runner.

BUG=chromium:374740
LOG=n
TEST=python -m unittest run_perf_test
TBR=ulan@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/776873005

Cr-Commit-Position: refs/heads/master@{#25651}