Implement a policy to autologin a public account.

chrome/browser/policy/proto/chrome_device_policy.proto

Index: chrome/browser/policy/proto/chrome_device_policy.proto
diff --git a/chrome/browser/policy/proto/chrome_device_policy.proto b/chrome/browser/policy/proto/chrome_device_policy.proto
index 0e9863e2cd612f655f584d62731bddb6937b93f2..0b45bdf5cca4f7e1d9edc4bba8f7a4cd064988ac 100644
--- a/chrome/browser/policy/proto/chrome_device_policy.proto
+++ b/chrome/browser/policy/proto/chrome_device_policy.proto
@@ -235,6 +235,17 @@ message DeviceLocalAccountsProto {
   // The list of device-local accounts (i.e. accounts without an associated
   // cloud-backed profile) that are available on the device.
   repeated DeviceLocalAccountInfoProto account = 1;
+
+  // The identifier of the device-local account to which the device
+  // should be logged in automatically.
+  optional string auto_login_id = 2;
+
+  // The amount of time that should elapse at the signin screen before
+  // automatically logging in.
+  optional int64 auto_login_delay = 3;
+}
+
+message DeviceLocalAccountAutoLoginProto {
 }
 
 message ChromeDeviceSettingsProto {