however required a unlocked boot loader.
you can use TWRP file manager to replace below files. (hence not needing root).
(or someone can kindly create a flashable)
I have recomplied the power.shamu.so (replacing the missing codes from https://android.googlesource.com/dev...cf7cace%5E%21/ )
What this does is also re-enable the double-tap to wake.
backup a copy of
then copy the attached power.shamu.so to /system/lib/hw/
change the permission of power.shamu.so to 0644
then boot your device. volia... you now have double tap to wake again.
Note. this has been tested with my own nexus 6.