The script prints a bunch of stuff behind `if verbose` checks, but then
"verbose" was turned on by default in
https://bugs.chromium.org/p/chromium/issues/detail?id=504452

I think the wrong lesson was learned from that bug – it sounds like the
problem was that an error message was printed only if verbose was set.
After this change, the script is silent when it does nothing, and prints
something if something happens. (Arguably, it still prints too much in the
case where it successfully downloads something.)

This is part of a few changes to make `gclient runhooks` less noisy.

Bug: 772741,504452
Change-Id: I5823c296abe97611ba4411bab2743673b10dca4b
Reviewed-on: https://chromium-review.googlesource.com/706915
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Ryan Tseng <hinoka@chromium.org>