deps: backport 2bcbe2f from V8 upstream

[ofrobots]

Checklist

• make -j4 test (UNIX), or vcbuild test nosign (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

Excessive buffering of perf map files in V8 could cause profiles to be missing symbols at times. Original commit message: switch perf and ll_prof loggers to line buffering BUG=v8:5015 [email protected],[email protected] Review-Url: https://codereview.chromium.org/2041243002 Cr-Commit-Position: refs/heads/master@{#36788} 

Note that this is not needed on master as V8 5.1 already contains this fix.
R=@nodejs/v8

EDIT: CI: https://ci.nodejs.org/job/node-test-pull-request/3362/

[bnoordhuis]

LGTM but out of curiosity, is there a reason you opted for line buffering instead of no buffering? It seems the output is line oriented anyways so libc's newline scanning just adds unnecessary, if minimal, overhead.

[ofrobots]

No strong reason other than to avoid any file watchers from observing partially complete lines. The output is indeed line oriented today; but the code may change in the future. The new line scanning is going to be negligible cost.

[ofrobots]

Rebased, added a V8 patch-level bump. Relaunched CI: https://ci.nodejs.org/job/node-test-pull-request/3413/.

[ofrobots]

V8 CI: https://ci.nodejs.org/job/node-test-commit-v8-linux/244/. I think the Power BE machine has infrastructure issues. The rest are green.

[ofrobots]

@nodejs/release: this is ready for landing onto v6.x. Should I do that myself?

[evanlucas]

works for me :]

[ofrobots]

Thanks. Landed on v6.x as e82e804.