Added support for signed policy blobs on desktop.

components/policy/proto/policy_signing_key.proto

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+package enterprise_management;
+
+// Contains a signing key and its signature.
+message PolicySigningKey {
+  // The key used to verify policy blobs sent down from the server.
+  optional bytes signing_key = 1;
+
+  // The signature for this signing key (verified using a hard-coded key
+  // stored in the Chrome binary).
+  optional bytes signing_key_signature = 2;

[Mattias Nissler (ping if slow), 2014/01/27 13:52:13]

Suggestion: Rename this to signing_key_certificate? IMHO, that'd be closer to
the standard terms and thus pressing the right buttons in one's mental state.

[Andrew T Wilson (Slow), 2014/01/30 17:10:31]

I'll add a comment. We already using _signature in other places in our protos
for similar situations (think of new_public_key_signature) so I'll keep this
name for now.

+}