Teach PRESUBMIT.py how to run gn check for most of the mojo repo

Almost all of the mojo-forked code now passes gn check.
I used:
https://github.com/domokit/mojo/wiki/Directory-guide
for the list of mojo-forked directories.

gn check //mojo/* was 152 errors and is now down to 52.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/707093002