Should be tracking scrolls for Outer, and not Inner, scroll layer.

Should be tracking scrolls for Outer, and not Inner, Viewport.

In https://codereview.chromium.org/1013753014 the trace added to track
main-frame scrolling was watching on the wrong viewport layer. This CL
fixes it so it watches the OuterViewportLayer instead.

BUG=468304
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Committed: https://crrev.com/3233269d7dd4ff4403f047fd32df0bd97a4f0257
Cr-Commit-Position: refs/heads/master@{#339951}

[wjmaclean, 2015-07-22 18:50:11]

wjmaclean@chromium.org changed reviewers:
+ enne@chromium.org

[wjmaclean, 2015-07-22 18:50:11]

One-liner, TRACE fix, please take a  look?

[wjmaclean, 2015-07-22 18:50:24]

The CQ bit was checked by wjmaclean@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-07-22 18:51:00]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1244143003/1

[enne (OOO), 2015-07-22 19:00:42]

lgtm

[commit-bot: I haz the power, 2015-07-22 19:51:02]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-07-22 19:51:03]

Dry run: This issue passed the CQ dry run.

[wjmaclean, 2015-07-22 20:34:24]

The CQ bit was checked by wjmaclean@chromium.org

[commit-bot: I haz the power, 2015-07-22 20:35:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1244143003/1

[commit-bot: I haz the power, 2015-07-22 20:48:51]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-22 20:49:39]

Patchset 1 (id:??) landed as
https://crrev.com/3233269d7dd4ff4403f047fd32df0bd97a4f0257
Cr-Commit-Position: refs/heads/master@{#339951}