Add PID info into ANR crash log header

For improvement of crash log analysis, add a PID info of the target
process into ANR dropbox crash log header.

In the ANR dropbox crash log, sometimes the process name (Cmd line)
in a stacktrace section is not an actual app process name, but is
"zygote" or "<pre-initialized>" instead. This may be caused when App
ANR happened just after an app process is started. Hence the
stacktrace of target app process cannot be found by process
name at crash log analysis. If PID info is provided, it can be used
to find the stacktrace section instead of the process name.

Bug: 28713716
Change-Id: I28624f2b3c8bc0e8b7545de9525a68bad420d6a0