trigger kernel blocked stack trace on system server watchdog

Bug b/7638530 may be caused by a kernel deadlock when killing
processes under low memory conditions.  Write to /proc/sysrq-trigger
to get a kernel log of blocked tasks before killing the system server.

Bug: 7638530
Change-Id: I60df324ad4affdadbf13650099dc4dfb38722420
1 file changed