Remove crash expectations for line-height animation

These tests are no longer crashing in debug:
animations/interpolation/line-height-interpolation.html
virtual/threaded/animations/interpolation/line-height-interpolation.html

Flakiness dashboard:
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&tests=line-height-interpolation.html

BUG=303430

Review URL: https://codereview.chromium.org/68983005

git-svn-id: svn://svn.chromium.org/blink/trunk@161879 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Update the accessibility tree when a modal dialog is opened/closed.

This patch is an improved approach from r161595. It turns out it's not
sufficient to traverse the new AT tree calling
notifyIfIgnoreValueChanged on each node, since the browser-side can hold
on to descendents that have been pruned out of the tree and never get a
child changed notification for them.

This patch blows away the entire tree and forces it to rebuild when a
modal dialog is opened/closed. It's a big hammer but seems to be the
most foolproof approach. We considered approaches like traversing
m_objects calling notifyIfIgnoreValueChanged on each, but it's
conceivable that m_objects isn't up-to-date. Since a modal dialog likely
causes a massive change to the tree, starting over entirely isn't so
inefficient.

The test for this patch is Chrome-side:
https://codereview.chromium.org/64273003/

This patch causes inert-node-is-hidden.html to fail, because
AccessibilityController doesn't expect the AX cache to get destroyed
and recreated. Since the DumpAccessibilityTree tests on Chrome-side
cover the behavior and the plan is to have only DumpAccessibilityTree
tests in the future, I'm removing inert-node-is-hidden.html.

BUG=304779

Review URL: https://codereview.chromium.org/70213002

git-svn-id: svn://svn.chromium.org/blink/trunk@161880 bbb929c8-8fbe-4397-9dbb-9b2b20218538