tools/gn: Fix more "propogated" typos.

The correct spelling is "propagated".

BUG=None
R=brettw@chromium.org

Review URL: https://codereview.chromium.org/1381473002

Cr-Original-Commit-Position: refs/heads/master@{#351377}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 1e44f96c65cf0cff3534a2e53930ef65ed2b5e55