output flags once

When asking for help on more than one item,
e.g. foo -h me -h oh -h my just print Flags:
once.

TBR=scroggo@google.com

Change-Id: I67080c7390e6bacf4c36096304dd959229fdd07b
Reviewed-on: https://skia-review.googlesource.com/21660
Reviewed-by: Cary Clark <caryclark@skia.org>
Commit-Queue: Cary Clark <caryclark@skia.org>
1 file changed