[turbofan] Make Factory::NewNumber() always return the minus_zero_value.

[turbofan] Make Factory::NewNumber() always return the minus_zero_value.

TEST=unittests
R=mstarzinger@chromium.org, dcarney@chromium.org

Committed: https://crrev.com/55b3e268b2895e2c09230d39669a75b6ab4e7e4d
Cr-Commit-Position: refs/heads/master@{#26080}

[Benedikt Meurer, 2015-01-15 15:00:48]

PTAL

[Michael Starzinger, 2015-01-15 15:08:30]

mstarzinger@chromium.org changed reviewers:
+ mstarzinger@chromium.org

[Michael Starzinger, 2015-01-15 15:08:30]

LGTM.

[Benedikt Meurer, 2015-01-15 15:09:31]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2015-01-15 15:09:40]

The CQ bit was unchecked by bmeurer@chromium.org

[Benedikt Meurer, 2015-01-15 15:10:11]

Committed patchset #1 (id:1) manually as
55b3e268b2895e2c09230d39669a75b6ab4e7e4d (presubmit successful).

[commit-bot: I haz the power, 2015-01-15 15:10:13]

Patchset 1 (id:??) landed as
https://crrev.com/55b3e268b2895e2c09230d39669a75b6ab4e7e4d
Cr-Commit-Position: refs/heads/master@{#26080}

[Benedikt Meurer, 2015-01-15 15:28:37]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/853683009/ by bmeurer@chromium.org.

The reason for reverting is: Breaks the tree.