[protosync] Server-side -> client

Sync server-side changes from
https://critique.corp.google.com/#review/244290147 to client.

Bug: None
Change-Id: Id6377e63ba66f2177a44d26462dd6d4506832482
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1624568
Auto-Submit: Jit Yao Yap <jityao@google.com>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662137}

components/policy/proto/device_management_backend.proto

@@ -654,6 +654,11 @@ message PolicyFetchResponse {
   // new_public_key_signature).
   // See http://go/chrome-nac-server-design for more information.
   optional bytes new_public_key_verification_data_signature = 9;
+
+  // See PolicyFetchRequest.policy_type. This field is NOT signed by DMServer
+  // and is informational only. Client-side should verify and rely on the
+  // policy_type inside the signed policy_data.
+  optional string policy_type = 10;
 }
 
 // DEPRECATED: Protobuf used to generate the deprecated