[turbofan] Improve typing of ToBoolean.

[turbofan] Improve typing of ToBoolean.

According to ES6 draft, revision 29 (2014-12-06), section 7.1.2,
ToBoolean yields true for true, detectable receivers (the ES6 Object
type), symbols and numbers except -0, +0 and NaN.

R=hpayer@chromium.org

Committed: https://crrev.com/1ed16c587e3187bad0405abad2403d6a2a8cbac3
Cr-Commit-Position: refs/heads/master@{#25915}

[Benedikt Meurer, 2014-12-22 06:44:12]

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

[Benedikt Meurer, 2014-12-22 06:44:13]

PTAL

Reference documentation (current ES6 draft) for ToBoolean:
https://people.mozilla.org/~jorendorff/es6-draft.html#sec-toboolean

[Hannes Payer (out of office), 2014-12-22 06:50:25]

lgtm

[Benedikt Meurer, 2014-12-22 07:21:59]

Committed patchset #1 (id:1) manually as
1ed16c587e3187bad0405abad2403d6a2a8cbac3 (presubmit successful).

[commit-bot: I haz the power, 2014-12-22 07:22:01]

Patchset 1 (id:??) landed as
https://crrev.com/1ed16c587e3187bad0405abad2403d6a2a8cbac3
Cr-Commit-Position: refs/heads/master@{#25915}