It should be possible to create a concise method with the name
__proto__ without setting the [[Prototype]]. Similarly, property
name shorthands with the name __proto__ should define an own
property.
BUG=v8:3818
LOG=Y
R=adamk, dslomov@chromium.org
Review URL: https://codereview.chromium.org/858673002
Cr-Commit-Position: refs/heads/master@{#26172}