drop __proto__ usage
drop __proto__ usage

The __proto__ member is non-standard and inconsistent across JS
implementations.  Switch to the ES5 standard method for inheriting
object prototypes.

Change-Id: Iff536a891c2f0e3eedd6bcc9c6255f4328427b08
Reviewed-on: https://chromium-review.googlesource.com/509194
Reviewed-by: Brandon Gilmore <adbfbaf7e4f927b45ce8ad3e5043a632414a833b@google.com>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

chromium/hterm,chromium/hterm,chromium/hterm,chromium/hterm