BaseDragLayer only lets the top AFV intercpet touch events, otherwise it
moves onto its TouchController instances. Taskbar AllApps still needs to
intercept touch events sometimes when an AFV above it cannot (e.g. a
snackbar). This CL adds a TouchController to TaskbarOverlayDragLayer
that delegates to TaskbarAllAppsSlideInView if it is open.
Test: Manual
Fix: 299165179
Flag: No
Change-Id: I9b73c55f698de5b60b463f91140a6717a7053cd3
Brian Isganitis
91a4aca5a5