Print detailed info in check_gn_headers.py

When --verbose is given, print more detailed info to help debugging.
The dependency of offending header files and the obj files they affect
should help determine which files to fix. The number of affected
object files can be a proxy of seriousness.

If the whitelist is not given, the extra detail would be very long.

BUG=661774
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_chromium_dbg_ng

Review-Url: https://codereview.chromium.org/2932153002
Cr-Commit-Position: refs/heads/master@{#478956}
3 files changed