Mark emergency gesture container view unimportant for a11y.

Similar to change I415090fb8601bc4cb129999a50ac35e045ef7830, the
container has nothing meaningful for accessibility tools. Marking it
unimportant forces children view's accessibility events to show up.

Fix: 175515538
Fix: 175515122
Test: manual
Change-Id: Ib9c9b67622f7ea67368dc3fe04c78c984b70c7e5