[turbofan] Improve typed lowering for JSToBoolean.

[turbofan] Improve typed lowering for JSToBoolean.

- JSToBoolean(x:string) => BooleanNot(NumberEqual(x.length, #0))
- JSToBoolean(phi(x1,...,xn):primitive) => phi(JSToBoolean(x1),...,JSToBoolean(xn))

TEST=cctest,mjsunit/asm/do-while,mjsunit/boolean,unittests
R=dcarney@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=24919

[Benedikt Meurer, 2014-10-28 08:29:27]

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

[Benedikt Meurer, 2014-10-28 08:29:27]

PTAL

[dcarney, 2014-10-28 08:31:55]

lgtm

[Benedikt Meurer, 2014-10-28 08:34:06]

Committed patchset #1 (id:1) manually as 24919 (presubmit successful).