this version of init contains code to perform "bootcharting", i.e. generating log
files that can be later processed by the tools provided by www.bootchart.org.

to activate it, you need to define build 'init' with the INIT_BOOTCHART environment
variable defined to 'true', then create a file on the /data partition with a command
like the following:

  adb shell 'echo 1 > /data/bootchart'

if the '/data/bootchart' file doesn't exist, or doesn't contain a '1' in its first
byte, init will proceed normally.

by default, the bootchart log stops after 2 minutes, but you can stop it earlier
with the following command while the device is booting:

  adb shell 'echo 1 > /data/bootchart-stop'

note that /data/bootchart-stop is deleted automatically by init at the end of the
bootcharting. this is not the case of /data/bootchart, so don't forget to delete it
when you're done collecting data:

  adb shell rm /data/bootchart

the log files are placed in /tmp/bootchart/. you must run the script tools/grab-bootchart.sh
which will use ADB to retrieve them and create a bootchart.tgz file that can be used with
the bootchart parser/renderer, or even uploaded directly to the form located at:

  http://www.bootchart.org/download.html

technical note:

this implementation of bootcharting does use the 'bootchartd' script provided by
www.bootchart.org, but a C re-implementation that is directly compiled into our init
program.