cros: Add app_to_pin_os policy

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 d8e48b5a2c53b976940194ae22b2e1074e416597..78187e5a6896e676819677ae43fd6208b85abff0 100644
--- a/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
+++ b/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
@@ -794,6 +794,13 @@ message DeviceEcryptfsMigrationStrategyProto {
   optional MigrationStrategy migration_strategy = 1;
 }
 
+// An app on Chrome Web Store whose manifest key "required_platform_version"
+// value would be used as the OS pin. Note the app does not have to be present
+// on the device. The pin is applied on the server side.
+message AppToPinOS {
+  optional string app_id = 1;
+}
+
 message ChromeDeviceSettingsProto {
   optional DevicePolicyRefreshRateProto device_policy_refresh_rate = 1;
   optional UserWhitelistProto user_whitelist = 2;
@@ -854,4 +861,5 @@ message ChromeDeviceSettingsProto {
   optional LoginScreenInputMethodsProto login_screen_input_methods = 50;
   optional DeviceEcryptfsMigrationStrategyProto
       device_ecryptfs_migration_strategy = 51;
+  optional AppToPinOS app_to_pin_os = 52;
 }