Move observable changes into InkDropEventHandler

This specifically moves InkDropHostView::OnBoundsChanged and
::VisibilityChanged into InkDropEventHandler, using the corresponding
ViewObserver APIs.

Note that there's no API corresponding to ::ViewHierarchyChanged so a
TODO is left to make sure that we can observe when the host gets removed
from the hierarchy.

Bug: chromium:939419
Change-Id: Iec2d36cd1977afe9ede897e753fd95b3069986dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1521961
Reviewed-by: Collin Baker <collinbaker@chromium.org>
Commit-Queue: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641753}
4 files changed