GitLab

Changes:
1. Avoid calculating and updating opacity for all apps for each dragging
   update. Instead, calculate opacity of each row in current page and
   only update changed apps. Also avoid button press on page switcher
   during dragging to prevent opacity not being reset.
2. Clear search results after widget has been destroyed to avoid jank
   during close animation.

Bug: 897384
Change-Id: Id0e848cc82f60740212467c64e05d032081ad45b
Reviewed-on: https://chromium-review.googlesource.com/c/1292386Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Yury Khmel <khmel@chromium.org>
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601755}