Allow the use of debug.db.uid on userdebug / eng builds.
Setting this property allows debuggerd to suspend a process
if it detects a crash.

Make debug.db.uid only accessible to the su domain. This should
not be used on a user build.

Only support reading user input on userdebug / eng builds.

Steps to reproduce with the "crasher" program:

  adb root
  adb shell setprop debug.db.uid 20000
  mmm system/core/debuggerd
  adb sync
  adb shell crasher

Addresses the following denials:

<5>[  580.637442] type=1400 audit(1392412124.612:149): avc:  denied  { read } for  pid=182 comm="debuggerd" name="input" dev="tmpfs" ino=5665 scontext=u:r:debuggerd:s0 tcontext=u:object_r:input_device:s0 tclass=dir
<5>[  580.637589] type=1400 audit(1392412124.612:150): avc:  denied  { open } for  pid=182 comm="debuggerd" name="input" dev="tmpfs" ino=5665 scontext=u:r:debuggerd:s0 tcontext=u:object_r:input_device:s0 tclass=dir
<5>[  580.637706] type=1400 audit(1392412124.612:151): avc:  denied  { read write } for  pid=182 comm="debuggerd" name="event5" dev="tmpfs" ino=6723 scontext=u:r:debuggerd:s0 tcontext=u:object_r:input_device:s0 tclass=chr_file
<5>[  580.637823] type=1400 audit(1392412124.612:152): avc:  denied  { open } for  pid=182 comm="debuggerd" name="event5" dev="tmpfs" ino=6723 scontext=u:r:debuggerd:s0 tcontext=u:object_r:input_device:s0 tclass=chr_file
<5>[  580.637958] type=1400 audit(1392412124.612:153): avc:  denied  { ioctl } for  pid=182 comm="debuggerd" path="/dev/input/event5" dev="tmpfs" ino=6723 scontext=u:r:debuggerd:s0 tcontext=u:object_r:input_device:s0 tclass=chr_file

Bug: 12532622
Change-Id: I63486edb73efb1ca12e9eb1994ac9e389251a3f1