Move unit tests to test/unittests.

Move unit tests to test/unittests.

As per discussion on the V8 team, this is the place we want them to live,
not following the Chrome Style Guide for this.

BUG=v8:3489
LOG=y
R=svenpanne@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=24350

[Benedikt Meurer, 2014-10-01 08:11:42]

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

[Benedikt Meurer, 2014-10-01 08:11:43]

PTAL

[Sven Panne, 2014-10-01 08:30:05]

LGTM (rubberstamped)

[Benedikt Meurer, 2014-10-01 08:35:45]

Committed patchset #2 (id:20001) manually as 24350 (presubmit successful).