Fix a couple of DCHECKs that could be hit with remote commands enabled.

1/ RemoteCommandsInvalidator needs its Shutdown method called before
   destruction.
2/ RemoteCommandsInvalidator calls Start() itself after initialization
   is complete, no need to call it manually.

Bug: 1137832
Change-Id: I4a76369100c2bc1d599ddb8b43fc055d6fd301d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2463715Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: anthonyvd <anthonyvd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816636}

chrome/browser/policy/chrome_browser_cloud_management_controller_desktop.cc

@@ -311,6 +311,8 @@ void ChromeBrowserCloudManagementControllerDesktop::OnServiceAccountSet(
 void ChromeBrowserCloudManagementControllerDesktop::ShutDown() {
   if (policy_invalidator_)
     policy_invalidator_->Shutdown();
+  if (commands_invalidator_)
+    commands_invalidator_->Shutdown();
 }
 
 MachineLevelUserCloudPolicyManager*
@@ -393,7 +395,6 @@ void ChromeBrowserCloudManagementControllerDesktop::StartInvalidations() {
             ->core(),
         base::DefaultClock::GetInstance(), PolicyInvalidationScope::kCBCM);
     commands_invalidator_->Initialize(invalidation_service_.get());
-    commands_invalidator_->Start();
   }
 }