Fix create OnScreen surface on Mac for compositor_unittests

Fix create OnScreen surface on Mac for compositor_unittests

After issue https://codereview.chromium.org/227473009 there is no code for
create OnScreen surface for Mac which is using in compositor_unittests.
Result:
18 tests crashed:
    LayerWithDelegateTest.ConvertPointToLayer_Medium
    LayerWithDelegateTest.ConvertPointToLayer_Simple
    LayerWithDelegateTest.DelegatedLayer
    LayerWithDelegateTest.SchedulePaintFromOnPaintLayer
    LayerWithDelegateTest.SetBoundsWhenInvisible
    LayerWithNullDelegateTest.SetBoundsSchedulesPaint
    LayerWithNullDelegateTest.Visibility
    LayerWithRealCompositorTest.CompositorObservers
    LayerWithRealCompositorTest.Delegate
    LayerWithRealCompositorTest.Draw
    LayerWithRealCompositorTest.DrawPixels
    LayerWithRealCompositorTest.DrawTree
    LayerWithRealCompositorTest.Hierarchy
    LayerWithRealCompositorTest.HierarchyNoTexture
    LayerWithRealCompositorTest.ModifyHierarchy
    LayerWithRealCompositorTest.Opacity
    LayerWithRealCompositorTest.ScaleReparent
    LayerWithRealCompositorTest.ScaleUpDown

If surface is created then all tests passed.

R=sievers@chromium.org, ccameron1@chromium.org, danakj@chromium.org

TEST=compositor_unittests

Committed: https://crrev.com/18499aa5a6af1ee9132436dd3a2fd3cbdb580918
Cr-Commit-Position: refs/heads/master@{#291863}

[no sievers, 2014-08-25 20:33:01]

lgtm

[piman, 2014-08-25 20:34:17]

lgtm

[Lof, 2014-08-26 05:22:27]

The CQ bit was checked by lof84@yandex-team.ru

[commit-bot: I haz the power, 2014-08-26 05:24:23]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/lof84@yandex-team.ru/504933002/1

[commit-bot: I haz the power, 2014-08-26 07:51:34]

Committed patchset #1 (1) as 1a7e0399a5e806268cd949d34ed022c1c51c3b1e

[commit-bot: I haz the power, 2014-09-10 02:41:16]

Patchset 1 (id:??) landed as
https://crrev.com/18499aa5a6af1ee9132436dd3a2fd3cbdb580918
Cr-Commit-Position: refs/heads/master@{#291863}