[depot_tools] Add "ensure_bootstrap" script.
[depot_tools] Add "ensure_bootstrap" script.

Add a "ensure_bootstrap" script, which syncs the bootstrapped state of
"depot_tools" so that remaining operations become read-only.

BUG=chromium:769369
TEST=local

Change-Id: I2dab36112b378a926d8201d2ab31a7daa9f5da29
Reviewed-on: https://chromium-review.googlesource.com/691318
Commit-Queue: Daniel Jacques <8400006a9338a0893dca0101ad49838955bd6b2c@chromium.org>
Reviewed-by: Don Garrett <546ec366615570e68497e3c5df9092106a9808f4@chromium.org>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools