Temporary fix for a crash at TouchActionFilter::ReportTouchAction

This is a temporary fix to ensure that there will be no crash at
TouchActionFilter::ReportTouchAction when the |scrolling_touch_action_|
has no value.

TBR=nzolghadr@chromium.org

Bug: 879511
Change-Id: I90aa531db743fb989855b2fd42a9a10bf0578561
Reviewed-on: https://chromium-review.googlesource.com/1227234
Commit-Queue: Xida Chen <xidachen@chromium.org>
Reviewed-by: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#591662}
1 file changed