Add DeviceRegisterRequest.BROWSER and use it for chrome.

chrome/browser/policy/proto/device_management_backend.proto

 // Copyright (c) 2012 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;
 
 // Request from device to server to register device.
 message DeviceRegisterRequest {
   // Reregister device without erasing server state.  It can be used
   // to refresh dmtoken etc.  Client MUST set this value to true if it
   // reuses an existing device id.
   optional bool reregister = 1;
 
   // Device register type.  This field does not exist for TT release.
   // When a client requests for policies, server should verify the
   // client has been registered properly.  For example, a client must
   // register with type DEVICE in order to retrieve device policies.
   enum Type {
     TT   = 0;       // Register for TT release.
-    USER = 1;       // Register for user polices.
+    USER = 1;       // Register for Chrome OS user polices.
     DEVICE = 2;     // Register for device policies.
+    BROWSER = 3;    // Register for Chrome user policies.
   }
   // NOTE: we also use this field to detect client version.  If this
   // field is missing, then the request comes from TT.  We will remove
   // Chrome OS TT support once it is over.
   optional Type type = 2 [default = TT];
 
   // Machine hardware id, such as serial number.
   // This field is required if register type == DEVICE.
   optional string machine_id = 3;
 
@@ skipping 471 matching lines @@
 
   // Device status report response.
   optional DeviceStatusReportResponse device_status_report_response = 6;
 
   // Session status report response.
   optional SessionStatusReportResponse session_status_report_response = 7;
 
   // Auto-enrollment detection response.
   optional DeviceAutoEnrollmentResponse auto_enrollment_response = 8;
 }