Add a single-file viewer option

Pass --file/-f to open a single file for viewing.

Change-Id: Ida168765ed6a5c7d76df1a8298bfe658d39d0196
Reviewed-on: https://skia-review.googlesource.com/126761
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
1 file changed