Fix crash when shutting down affiliated invalidation service provider

When the affiliated invalidation service provider, it should:
1) unregister itself as an observer of various objects
2) tell consumers to stop using the current invalidation service
3) destroy the device-global invalidation service, if any

Steps 2 and 3 were swapped. This meant that if the device-global
invalidation service happened to be in use, it would be destroyed
without giving consumers a chance to remove their handlers from it.

BUG=455504
TEST=None

Review URL: https://codereview.chromium.org/942463002

Cr-Commit-Position: refs/heads/master@{#317017}

chrome/browser/chromeos/policy/affiliated_invalidation_service_provider_impl.cc

@@ -209,7 +209,7 @@ void AffiliatedInvalidationServiceProviderImpl::Shutdown() {
 
   registrar_.RemoveAll();
   profile_invalidation_service_observers_.clear();
-  DestroyDeviceInvalidationService();
+  device_invalidation_service_observer_.reset();
 
   if (invalidation_service_) {
     invalidation_service_ = nullptr;
@@ -217,6 +217,8 @@ void AffiliatedInvalidationServiceProviderImpl::Shutdown() {
     // is no longer available.
     SetInvalidationService(nullptr);
   }
+
+  DestroyDeviceInvalidationService();
 }
 
 invalidation::TiclInvalidationService*