Ensure that the auto scroll state in the AutoscrollController is cleared if the
scroll operation clears out the m_autoscrollLayoutObject member.
This typically happens when we scroll a div inside an iframe which uses
overflow:auto and during the scroll the cursor leaves the bounds of the div.
If we don't reset the state then the page gets stuck in the autoscroll state
causing it to be unresponsive to clicks etc.
BUG=336373
Review URL: https://codereview.chromium.org/1461473002
Cr-Commit-Position: refs/heads/master@{#360997}
4 files changed
