Do not disable guest mode when BrowserSignin override ForceBrowesrSignin without a forced value

Bug: 894212
Change-Id: Icd4c7d9f8a79a9b57900366d4677b0e7023b8ca3
Reviewed-on: https://chromium-review.googlesource.com/c/1274196
Commit-Queue: Owen Min <zmin@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599247}
2 files changed