Make unsafe Unique<T> constructor private.

Make unsafe Unique<T> constructor private.

The constructor taking an artificial raw address was only used as a
workaround in TurboFan. It should only be accessible by constructor
functions internal to Unique<T>.

R=titzer@chromium.org

Committed: https://crrev.com/0526e102d73c3253c3ad90350d774d36758a4278
Cr-Commit-Position: refs/heads/master@{#30464}

[titzer, 2015-08-31 09:55:44]

lgtm

[Michael Starzinger, 2015-08-31 10:12:54]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-08-31 10:13:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1326493002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1326493002/1

[commit-bot: I haz the power, 2015-08-31 10:44:11]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-31 10:44:27]

Patchset 1 (id:??) landed as
https://crrev.com/0526e102d73c3253c3ad90350d774d36758a4278
Cr-Commit-Position: refs/heads/master@{#30464}