v8: fix RegExp nits in v8_prof_polyfill.js

[vsemozhetbyt]

Checklist

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

Affected core subsystem(s)

v8

• Do not repeat RegExp creation in a cycle.
• Use sufficient string instead of RegExp in split().

I am not sure about the status of this lib file (it is excluded from linting and is not tested in common CI). I've stumbled upon these fragments in some recent overall RegExp checks. The fixes seem rather simple and safe, but please suggest the ways we should test them if needed.

[vsemozhetbyt]

cc @nodejs/v8, @nodejs/performance

[indutny]

LGTM

[vsemozhetbyt]

Landed in 6b9500b

[MylesBorins]

Should this be backported to v6.x?

[targos]

It cherry-picks cleanly. I don't think it could cause any issue.

[MylesBorins]

I landed this on v6.x-staging and it seems to have been responsible for some failures on AIX + certain flavors of windows. I've backed it out for now and doing testing to see if the suite passes with this temporarily removed

failure below

not ok 56 parallel/test-child-process-detached --- duration_ms: 0.820 severity: fail stack: |-

assert.js:81
  throw new assert.AssertionError({
  ^
AssertionError: Got unwanted exception..
    at _throws (assert.js:356:5)
    at Function.assert.doesNotThrow (assert.js:374:3)
    at process.<anonymous> (/home/iojs/build/workspace/node-test-commit-aix/nodes/aix61-ppc64/test/parallel/test-child-process-detached.js:22:10)
    at emitOne (events.js:101:20)
    at process.emit (events.js:188:7)

...

edit: appears unrelated. going to bisect on machine and likely reland soon

edit 2: relanded