Add a device setting that indicates dev mode blocking status.

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

Index: chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
diff --git a/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto b/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
index 52ccfa3ef9441705cf54f39a346a05297225da1a..180b57bdf4db2ab4879123fec13d86cc95850058 100644
--- a/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
+++ b/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
@@ -565,6 +565,14 @@ message AutoCleanupSettigsProto {
   optional string clean_up_strategy = 1;
 }
 
+// Settings that control low-level functions of the system.
+message SystemSettingsProto {
+  // Whether developer mode is allowed on the device. If the device owner sets
+  // this flag to true, the system will refuse to boot and show an error screen
+  // when the developer switch is turned on.
+  optional bool block_devmode = 1;
+}
+
 message ChromeDeviceSettingsProto {
   optional DevicePolicyRefreshRateProto device_policy_refresh_rate = 1;
   optional UserWhitelistProto user_whitelist = 2;
@@ -597,4 +605,5 @@ message ChromeDeviceSettingsProto {
   optional LoginScreenPowerManagementProto login_screen_power_management = 29;
   optional SystemUse24HourClockProto use_24hour_clock = 30;
   optional AutoCleanupSettigsProto auto_clean_up_settings = 31;
+  optional SystemSettingsProto system_settings = 32;
 }