Add CHROME_BROWSER value to DeviceServiceApiAccessRequest::DeviceType

This is a prerequisite to allow DeviceAccountInitializer to be used
on desktop to fetch authcodes for invalidations registration.

Bug: 1026261
Change-Id: I9db6fbe4c420b34b5cc734207d728cc67045a1a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2134188Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Commit-Queue: anthonyvd <anthonyvd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756244}

components/policy/proto/device_management_backend.proto

@@ -283,6 +283,9 @@ message DeviceServiceApiAccessRequest {
     // to access Google Docs.
     // Please see go/cros-demo-mode and go/demo-mode-account-brainstorm.
     CHROME_OS_DEMO_MODE = 2;
+    // Authcode will be used by the enterprise-managed Chrome Browser to
+    // register for policy invalidations. This is requested during enrollment.
+    CHROME_BROWSER = 3;
   }
 
   // Device type indicates the intended use of the auth code.