Migrate upgrade_detector code to new DM token class.

Migrates RetrieveDMToken call to use the new BrowserDMToken class.

Bug: 1020296
Change-Id: I384a64e4587915930817ad7a803484a0f9cc9a10
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1906626Reviewed-by: Tien Mai <tienmai@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Commit-Queue: Dominique Fauteux-Chapleau <domfc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713962}

chrome/browser/upgrade_detector/upgrade_detector_impl.cc

@@ -419,7 +419,9 @@ bool UpgradeDetectorImpl::DetectOutdatedInstall() {
 #if defined(OS_WIN)
     // Don't show the update bubbles to enterprise users.
     if (base::IsMachineExternallyManaged() ||
-        !policy::BrowserDMTokenStorage::Get()->RetrieveDMToken().empty()) {
+        policy::BrowserDMTokenStorage::Get()
+            ->RetrieveBrowserDMToken()
+            .is_valid()) {
       return false;
     }
 #endif