Fix dialog accessibility issues.

This CL fixes some accessibility issues that would happen with dialogs
launched by the DialogLaunchAnimator. See bugs for more info.

Bug: 204944038
Bug: 208951968
Bug: 208951526
Fixes: 204944038
Fixes: 208951968
Fixes: 208951526
Test: Manual
Change-Id: I35b12a6e2bb2c4ae8556178fb634deb963457db6