[Ozone] Fix DCHECK and check for scroll events as well

[Ozone] Fix DCHECK and check for scroll events as well

Scroll events are mouse events as well. On debug builds this DCHECK
would otherwise get triggered.

BUG=none
NOTRY=true

Committed: https://crrev.com/a7738c9de62e061649896353c9d3ebe5176ece07
Cr-Commit-Position: refs/heads/master@{#295772}

[dnicoara, 2014-09-19 19:27:36]

dnicoara@chromium.org changed reviewers:
+ spang@chromium.org

[spang, 2014-09-19 19:41:07]

lgtm

[dnicoara, 2014-09-19 20:41:39]

The CQ bit was checked by dnicoara@chromium.org

[commit-bot: I haz the power, 2014-09-19 20:43:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/590523004/1

[commit-bot: I haz the power, 2014-09-19 20:51:06]

Committed patchset #1 (id:1) as 78b643049dbad43ff78b89c714559ed1692f9092

[commit-bot: I haz the power, 2014-09-19 20:51:57]

Patchset 1 (id:??) landed as
https://crrev.com/a7738c9de62e061649896353c9d3ebe5176ece07
Cr-Commit-Position: refs/heads/master@{#295772}