/lib/udev/rules.d/61-mpu.rules is in ubuntu-defaults-nexus7 0.54.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | # do not edit this file, it will be overwritten on update
# Mark mpu6050 as an accelerometer so that gnome settings daemon looks at it
SUBSYSTEM=="iio", ATTR{name}=="mpu6050", ENV{ID_INPUT_ACCELEROMETER}="1"
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