Implement /proc/[pid]/statm.
Implement /proc/[pid]/statm.

PiperOrigin-RevId: 195893391
Change-Id: I645b7042d7f4f9dd54723afde3e5df0986e43160

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor