Add --overrides-only switch for `gn args`.

Specifying --overrides-only with --list will cause only build
arguments with overrides (e.g. from args.gn or //.gn) to get printed.

TEST=build gn; gn args --list --short --overrides-only

Change-Id: Ib6deff324841559a7785c2c62d1965ca31a80765
Reviewed-on: https://chromium-review.googlesource.com/642717
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Mike Bjorge <mbjorge@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#498611}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: fcbf3354655456f6c907f85eef7cfe84f982ac23
1 file changed
tree: 6645ed13d874bfde083318586dff8c2be7a25ff0
  1. tools/