Record WM_BOOT_ANIMATION_DONE in WindowManagerService

to track user-perceived boot performance. Even though we already
have BOOT_PROGRESS_ENABLE_SCREEN, that one is recorded before
WindowManagerService asks bootanim to exit. Since it takes a few
seconds for bootanim to exit (depending on desc.txt in the boot
animation zip file), WM_BOOT_ANIMATION_DONE would represent
user-perceived boot time better.

Bug: 21637637
Change-Id: I9d81dbf3fdb5dcd780e3fc3ca01c8ada4d6f16ef