- Activating a TrayBubbleView brings an Android window to onPause state.
- This CL sets can_set_activate to false and makes TrayBubbleView not
  activated by default.
- If the TrayBubbleView is not activated, it cannot capture key events
  for moving focus or closing the view by keyboard. TrayBubbleView tries
  to register accelerators at the global level to capture those key
  events.
- Activates the TrayBubbleView by default if keyboard navigation
  accessibility feature (e.g. spoken feedback) is enabled.

BUG=726588,731748
TEST=Follow steps described in the issue

Review-Url: https://codereview.chromium.org/2897553002
Cr-Commit-Position: refs/heads/master@{#481421}