Add default value to Lifetime enum.

Add unnecessary value containing "DEFAULT" in the name just to
make ProtoBestPractices check happy.

Bug: 704091
Change-Id: I99e62d9d711eef17a783408c0fbe62b115b7ac68
Reviewed-on: https://chromium-review.googlesource.com/951249Reviewed-by: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Drew Wilson <atwilson@chromium.org>
Commit-Queue: Denis Kuznetsov <antrim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543379}

components/policy/proto/device_management_backend.proto

@@ -40,7 +40,7 @@ message SignedData {
 
 // Request from device to server to register a device, user or browser.
 message DeviceRegisterRequest {
-  reserved 5;
+  reserved 5, 10;
 
   // Reregister device without erasing server state.  It can be used
   // to refresh dmtoken etc.  Client MUST set this value to true if it
@@ -131,14 +131,16 @@ message DeviceRegisterRequest {
 
   // Enumerates different expected lifetimes of registration.
   enum Lifetime {
-    // Default case, no expiration.
-    LIFETIME_INDEFINITE = 0;
+    // Default case.
+    LIFETIME_UNDEFINED = 0;
+    // No expiration, most of the registrations have this lifetime.
+    LIFETIME_INDEFINITE = 1;
     // Lifetime for ephemeral user policy registration.
-    LIFETIME_EPHEMERAL_USER = 1;
+    LIFETIME_EPHEMERAL_USER = 2;
   }
 
   // Indicates the expected lifetime of registration.
-  optional Lifetime lifetime = 10;
+  optional Lifetime lifetime = 11 [default = LIFETIME_INDEFINITE];
 }
 
 // Response from server to device register request.