Temporarily adds another constructor to Compositor

Temporarily adds another constructor to Compositor

I'm doing this to avoid a gargantuan patch (see
https://codereview.chromium.org/273073002/ for how out of control
everything is right now).

BUG=none
TEST=none
R=piman@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=271245

[piman, 2014-05-16 23:37:59]

LGTM

[sky, 2014-05-17 02:20:48]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2014-05-17 02:22:29]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/sky@chromium.org/285373012/20001

[commit-bot: I haz the power, 2014-05-17 08:25:20]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  android_dbg_triggered_tests on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_dbg_triggered...)
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)

[commit-bot: I haz the power, 2014-05-17 17:33:59]

Change committed as 271245