[DeviceSync v2] Add feature flag to deprecate v1 DeviceSync

During the first phase of the CryptAuth v2 DeviceSync rollout, v2
DeviceSync is enabled behind the flag kCryptAuthV2DeviceSync, and v1 and
v2 DeviceSync run in parallel, with their results consolidated into a
single set of device data. The second phase of the v2 DeviceSync rollout
deprecates v1 DeviceSync behind the flag kCryptAuthV1DeviceSyncDeprecate
that we add here.

Bug: 951969, 1019206
Change-Id: Ic13a709649e3d3d8dd855563b1a57abed8c599db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1899415
Commit-Queue: Josh Nohle <[email protected]>
Reviewed-by: Kyle Horimoto <[email protected]>
Cr-Commit-Position: refs/heads/master@{#713844}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index b2a6b027..2e4f95eddc 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1709,6 +1709,10 @@
      kOsCrOS,
      FEATURE_VALUE_TYPE(
          chromeos::features::kBluetoothAggressiveAppearanceFilter)},
+    {"cryptauth-v1-devicesync-deprecate",
+     flag_descriptions::kCryptAuthV1DeviceSyncDeprecateName,
+     flag_descriptions::kCryptAuthV1DeviceSyncDeprecateDescription, kOsCrOS,
+     FEATURE_VALUE_TYPE(chromeos::features::kCryptAuthV1DeviceSyncDeprecate)},
     {"cryptauth-v2-device-activity-status",
      flag_descriptions::kCryptAuthV2DeviceActivityStatusName,
      flag_descriptions::kCryptAuthV2DeviceActivityStatusDescription, kOsCrOS,