Port 4490ce85

Original commit message:
    Create proper initial map for original constructor (new.target) instead of doing prototype
    transition on the base constructor's initial map. This approach fixes in-object slack tracking
    for subclass instances.
    This CL also fixes subclassing from String.

    It also fixes typed array map smashing done during typed array initialization.

R=ishell@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=v8:3101, v8:3330, v8:4419
LOG=N

Review URL: https://codereview.chromium.org/1425353002

Cr-Commit-Position: refs/heads/master@{#31720}