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This CL modifies the PRESUBMIT.py files in directories which are likely
to affect the Chromium CQ. It changes it to require a git footer in CLs
which touch them, and adds an error message if the footer isn't present.
See the linked bug for more details on the production freeze.

No-Try: true
Ignore-CQ-Freeze: Implementing CQ Freeze
Bug: 1109980
Change-Id: Ibfd41a2a0cf7a8f3f0e6a1ad930e3e2e6b8407d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2320992Reviewed-by: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Stephen Martinis <martiniss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792269}