projector: add presubmit hook for metrics changes.

Add a presubmit hook to ensure that changes to metrics also
include a statement affirming that the author has updated the
metrics tracker.

Bug=b:271883148
Change-Id: Id3e4a8e17fa2ace5e4379c47988a7cae96a0eddb

Change-Id: Id3e4a8e17fa2ace5e4379c47988a7cae96a0eddb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4319528
Reviewed-by: Li Lin <llin@chromium.org>
Commit-Queue: Galen Corey <galenemco@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1116394}

ash/projector/PRESUBMIT.py

@@ -0,0 +1,30 @@
+# Copyright 2023 The Chromium Authors
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# Optional but recommended
+PRESUBMIT_VERSION = '2.0.0'
+
+# Mandatory: run under Python 3
+USE_PYTHON3 = True
+
+
+def CheckMetricsChangeHasTrackerUpdatedMessage(input_api, output_api):
+    """Reminder to update metrics tracker and verify in CL description."""
+    description = input_api.change.DescriptionText()
+    metrics_tracker_re = input_api.re.compile(
+        r'PROJECTOR_METRICS_TRACKER_UPDATED|NO_METRICS_CHANGED')
+    metrics_file_re = input_api.re.compile(
+        r'.*chromium\/src\/ash\/projector\/projector_metrics\.cc')
+    error_message = ("If this CL adds, changes, or deletes a metric, please\n"
+    "update go/projector-metrics-tracker before submitting, then add\n"
+    "PROJECTOR_METRICS_TRACKER_UPDATED to the CL description. If there are\n"
+    "no changes to metrics in this CL, add NO_METRICS_CHANGED to the CL\n"
+    "description.")
+
+    for f in input_api.change.AffectedFiles(include_deletes=True,
+                                            file_filter=None):
+        if metrics_file_re.match(f.AbsoluteLocalPath(
+        )) and not metrics_tracker_re.match(description):
+            return [output_api.PresubmitError(error_message)]
+    return []