deps: backport 1f8555 from v8's upstream

Original commit message:

    api: introduce SealHandleScope

    When debugging Handle leaks in io.js we found it very convenient to be
    able to Seal some specific (root in our case) scope to prevent Handle
    allocations in it, and easily find leakage.

    R=yangguo
    BUG=

    Review URL: https://codereview.chromium.org/1079713002

    Cr-Commit-Position: refs/heads/master@{#27766}

Should help us identify and fix Handle leaks in core and user-space code.

NOTE: Works only in Debug build now, but is still better than nothing.

PR-URL: https://github.com/iojs/io.js/pull/1395


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>