Fix folder issue in small display

Changes:
1. Instead of apply transform to apps grid, apply it to the
   AppListMainView when apps grid does not fit in small display.
2. Add a separate layer for AppListMainView.
3. Avoid converting point using transform by using local coordiates when
   calculating the page flip buffer and bottom drag buffer.
4. Clean up unused code.

Images:
https://screenshot.googleplex.com/XcFxsGn9wfJ
https://screenshot.googleplex.com/JkvuTu9FoZY
https://screenshot.googleplex.com/Yy6OZfD4NvL


Bug: 914509,913408
Change-Id: I2030e865b1da26f23940f64454ba7ce514e0e5cf
Reviewed-on: https://chromium-review.googlesource.com/c/1413136
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623760}
9 files changed