GitLab

1. Add TransitionAnimationObserver to layout app list at the end of
   animation to make sure child views are in right position.
2. Replace old expand arrow icon with Skia-drawn arrow and implement the
   new transition.
3. Change the layout of apps grid and make the rows and cols adaptive to
   the width and height.
4. Enlarge the folder icon.

Demo: https://drive.google.com/open?id=1xlGUpNv1X-s4D9mSjAPkyfZBMWhCjJag

Change-Id: I3bc86870c66d0b35b36a801c16befb2624a33a55
Reviewed-on: https://chromium-review.googlesource.com/1121547Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Yury Khmel <khmel@chromium.org>
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575868}