One of the ways I've been testing this is a vanilla debian stable chroot created using debootstrap.

If the system does not have pkg-config installed, "gn gen out/Release" fails:

ERROR at //build/config/linux/pkg_config.gni:103:17: Script returned non-zero exit code.
    pkgresult = exec_script(pkg_config_script, args, "value")
                ^----------
Current dir: /home/ph/chromium/src/out/Release/
Command: python -- /home/ph/chromium/src/build/config/linux/pkg-config.py -s /home/ph/chromium/src/build/linux/debian_jessie_amd64-sysroot -a x64 glib-2.0 gmodule-2.0 gobject-2.0 gthread-2.0
Returned 1.
stderr:

Traceback (most recent call last):
  File "/home/ph/chromium/src/build/config/linux/pkg-config.py", line 223, in <module>
    sys.exit(main())
  File "/home/ph/chromium/src/build/config/linux/pkg-config.py", line 142, in main
    prefix = GetPkgConfigPrefixToStrip(options, args)
  File "/home/ph/chromium/src/build/config/linux/pkg-config.py", line 81, in GetPkgConfigPrefixToStrip
    prefix = subprocess.check_output(argv, env=os.environ)
  File "/usr/lib/python2.7/subprocess.py", line 212, in check_output
    process = Popen(stdout=PIPE, *popenargs, **kwargs)
  File "/usr/lib/python2.7/subprocess.py", line 390, in __init__
    errread, errwrite)
  File "/usr/lib/python2.7/subprocess.py", line 1024, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

See //build/config/linux/BUILD.gn:83:3: whence it was called.
  pkg_config("glib") {
  ^-------------------
See //ui/gfx/BUILD.gn:382:18: which caused the file to be included.
    configs += [ "//build/config/linux:x11" ]
                 ^-------------------------