Remove support for CompositingReasonPositionSticky

Remove support for CompositingReasonPositionSticky

Our support for position: sticky isn't even in the experimental feature set. We
shouldn't be burning time during every frame checking whether any RenderLayers
have sticky position.

R=esprehn@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175992

[abarth-chromium, 2014-06-12 00:13:12]

Yes, this feature appears to be completely untested.

[esprehn, 2014-06-12 00:21:25]

On 2014/06/12 at 00:13:12, abarth wrote:
> Yes, this feature appears to be completely untested.

Sadness. How many position: sticky tests do we have?

lgtm

[abarth-chromium, 2014-06-12 02:02:20]

On 2014/06/12 at 00:21:25, esprehn wrote:
> On 2014/06/12 at 00:13:12, abarth wrote:
> > Yes, this feature appears to be completely untested.
> 
> Sadness. How many position: sticky tests do we have?

I'm not sure, but apparently zero that test the compositing integration.  Note:
I don't think the compositor understands position: sticky anyway.

[abarth-chromium, 2014-06-12 02:02:35]

The CQ bit was checked by abarth@chromium.org

[commit-bot: I haz the power, 2014-06-12 02:03:56]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/abarth@chromium.org/328263002/1

[abarth-chromium, 2014-06-12 03:32:51]

The CQ bit was unchecked by abarth@chromium.org

[abarth-chromium, 2014-06-12 03:32:54]

The CQ bit was checked by abarth@chromium.org

[commit-bot: I haz the power, 2014-06-12 03:33:48]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/abarth@chromium.org/328263002/1

[commit-bot: I haz the power, 2014-06-12 05:44:35]

Change committed as 175992