[turbofan] Cache float32 constants on the JSGraph level.

[turbofan] Cache float32 constants on the JSGraph level.

Also slightly refactor the NodeCache and CommonNodeCache classes to
reduce inherent overhead of caching.

TEST=cctest

Committed: https://crrev.com/4f9193e047d50b1ffbca95e8185576af82c722b3
Cr-Commit-Position: refs/heads/master@{#25937}

[Benedikt Meurer, 2014-12-23 12:57:18]

bmeurer@chromium.org changed reviewers:
+ ishell@chromium.org

[Benedikt Meurer, 2014-12-23 12:57:18]

PTAL

[Igor Sheludko, 2014-12-23 13:44:46]

lgtm

[Igor Sheludko, 2014-12-23 13:44:51]

The CQ bit was checked by ishell@chromium.org

[commit-bot: I haz the power, 2014-12-23 13:45:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/822923002/1

[commit-bot: I haz the power, 2014-12-23 14:12:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-23 14:12:28]

Patchset 1 (id:??) landed as
https://crrev.com/4f9193e047d50b1ffbca95e8185576af82c722b3
Cr-Commit-Position: refs/heads/master@{#25937}