Custom buttons should only handle accelerators when focused.

BUG=541415

Review URL: https://codereview.chromium.org/1437523005

Cr-Commit-Position: refs/heads/master@{#360130}
void CustomButton::StopThrobbing() {
  if (hover_animation_->is_animating()) {
    hover_animation_->Stop();
    SchedulePaint();
  }
}

void CustomButton::StopThrobbing() {
  if (hover_animation_->is_animating()) {
    hover_animation_->Stop();
    SchedulePaint();
  }
}
