Added policy for disabling locally managed users.

chrome/browser/policy/proto/chromeos/chrome_device_policy.proto

Index: chrome/browser/policy/proto/chromeos/chrome_device_policy.proto
diff --git a/chrome/browser/policy/proto/chromeos/chrome_device_policy.proto b/chrome/browser/policy/proto/chromeos/chrome_device_policy.proto
index 2ba6519e1906761269bb48211fa175087b56b53b..65fe798869d85eab827cf573da5d429538554d75 100644
--- a/chrome/browser/policy/proto/chromeos/chrome_device_policy.proto
+++ b/chrome/browser/policy/proto/chromeos/chrome_device_policy.proto
@@ -408,6 +408,11 @@ message AccessibilitySettingsProto {
   optional ScreenMagnifierType login_screen_default_screen_magnifier_type = 4;
 }
 
+message SupervisedUsersSettingsProto {
+  // Defines whether supervised users can be created on the device.
+  optional bool supervised_users_enabled = 1;
+}
+
 message ChromeDeviceSettingsProto {
   optional DevicePolicyRefreshRateProto device_policy_refresh_rate = 1;
   optional UserWhitelistProto user_whitelist = 2;
@@ -436,4 +441,5 @@ message ChromeDeviceSettingsProto {
   optional VariationsParameterProto variations_parameter = 25;
   optional AttestationSettingsProto attestation_settings = 26;
   optional AccessibilitySettingsProto accessibility_settings = 27;
+  optional SupervisedUsersSettingsProto supervised_users_settings = 28;
 }