run-bindings-tests: better error message

run-bindings-tests: better error message

Bindings test results can get out of sync, causing mysterious failures,
as per thread "git cl upload > run-bindings-tests failed"
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/hQ2hqTZyLOw

This gives a more useful error message, explaining how to fix the problem.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=160540

[Nils Barth (inactive), 2013-10-25 02:12:16]

Adam, haraken,
error message fix so r-b-t failures are less confusing;
how does it look?

[abarth-chromium, 2013-10-25 02:19:11]

This looks great.  Thanks!  LGTM

[commit-bot: I haz the power, 2013-10-25 03:16:09]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/nbarth@chromium.org/43033002/1

[haraken, 2013-10-25 05:05:00]

LGTM

[commit-bot: I haz the power, 2013-10-25 05:05:16]

Change committed as 160540