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). This is essentially a certificate (key
+  // signed with another well-known key that establishes a trust root).
+  optional bytes signing_key_signature = 2;
+}