gclient: enable syntax validation by default
gclient: enable syntax validation by default

Please pass --disable-syntax-validation as an escape hatch.

Bug: 570091
Change-Id: Iceadc0d2fc54ca68e775c3bc7590f4329ddb4951
Reviewed-on: https://chromium-review.googlesource.com/509451
Commit-Queue: Paweł Hajdan Jr. <84cab74a96a175cf90ed68b8abab420352923e11@chromium.org>
Reviewed-by: Dirk Pranke <6693ee08b084bb2ffa767f664c99b689395e0e4b@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools