ChromeOS performance tests

Generating a Bootchart

Enable the bootchart feature when building the image by setting the following variable in the ChromeOS chroot prior to building an image.
```
export USE="bootchart"
```
You may want to add in any other features separated by spaces such as chrome-internal.
Build the image and flash it onto a device.
Setup the device state the way you desire it to be tested. This involves creating any user accounts and enabling any features necessary to see the particular boot sequence desired. For example, enabling ARC++ for a user.
Reboot the device and wait for it to finish booting.
Copy /var/log/bootchart/boot-YYYYMMDD-hhmmss.tgz to your host machine (scp works for this purpose).
Install pybootchartgui on your host system outside the change root and run the following command to generate a bootchart.png file:
```
pybootchartgui boot-YYYYMMDD-hhmmss.tar.gz
```