[turbofan] Prepare mechanism to enable TF on language subset.

[turbofan] Prepare mechanism to enable TF on language subset.

This allows enabling TurboFan on a certain subset of language features
in the AstNumberingVisitor. The heuristics of when to optimize remain
unchanged, only the choice of which optimizing compiler to use changes.

R=bmeurer@chromium.org
BUG=v8:4131
LOG=N

Committed: https://crrev.com/54b34bdd33e2bdc9169c363655796fba6feb0a09
Cr-Commit-Position: refs/heads/master@{#28544}

[Benedikt Meurer, 2015-05-21 10:55:04]

LGTM.

https://codereview.chromium.org/1155503002/diff/1/src/compiler.cc
File src/compiler.cc (right):

https://codereview.chromium.org/1155503002/diff/1/src/compiler.cc#newcode380
src/compiler.cc:380: (dont_crankshaft && strcmp(FLAG_turbo_filter, "~~") == 0)
||
This broke my heart...

[Michael Starzinger, 2015-05-21 11:25:18]

The CQ bit was checked by mstarzinger@chromium.org

[Michael Starzinger, 2015-05-21 11:25:18]

The patchset sent to the CQ was uploaded after l-g-t-m from bmeurer@chromium.org
Link to the patchset: https://codereview.chromium.org/1155503002/#ps20001
(title: "Fix think'o!")

[commit-bot: I haz the power, 2015-05-21 11:25:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1155503002/20001

[commit-bot: I haz the power, 2015-05-21 11:41:20]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-21 11:41:35]

Patchset 2 (id:??) landed as
https://crrev.com/54b34bdd33e2bdc9169c363655796fba6feb0a09
Cr-Commit-Position: refs/heads/master@{#28544}