cros: move ShowAccessibilityNotification to A11yController

Remove ShowAccessibilityNotification in AccessibilityObserver. That is
only used in TrayAccessibility, while TrayAccessibility should be pure
views code. Move the function and tests to AccessibilityController.

Bug: 800270
Test: covered by tests
Change-Id: I0551c8b36d1a4bfb030b786bd78d610627113828
Reviewed-by: Dominic Mazzoni <>
Reviewed-by: Xiyuan Xia <>
Commit-Queue: Qiang Xu <>
Cr-Commit-Position: refs/heads/master@{#551253}
7 files changed