Disallow Object.observe calls on access-checked objects (Chromium issue 531891).

Implement V8 extras utils object (issue 4276).

ES6: Array.prototype.slice and friends should use ToLength instead of ToUint32 (issue 3087).

Avoid excessive data copying for ExternalStreamingStream::SetBookmark (issue 4422).

Performance and stability improvements on all platforms.

Cr-Commit-Position: refs/heads/4.7.57@{#1}
Cr-Branched-From: a6e00c6a9f5a8abf2747293d7452dd0cf572c99e-refs/heads/master@{#30785}