harmony-classes: Fix some issues with syntactic restriction on super(...).

R=arv@chromium.org
BUG=v8:3330
LOG=N

Review URL: https://codereview.chromium.org/770843002

Cr-Commit-Position: refs/heads/master@{#25589}
MIPS: Use weak cells in map checks in polymorphic ICs.

Port 45a36948e1bb0f02d395ecbcfe6306553898268b

Fix typo in the mips ports.

BUG=

Review URL: https://codereview.chromium.org/767623003

Cr-Commit-Position: refs/heads/master@{#25590}