[Sync] Clean up observers in ConfigurationRefresher

This is needed to enable DestroyProfileOnBrowserClose by default in
automated tests (crrev.com/c/2503629).

ConfigurationRefresher did not clean up its SyncObserver properly when
it received the OnSyncShutdown() event, causing a failed DCHECK() in
browser tests.

Bug: 88586
Change-Id: Ib37846afd26470563d58639e9fddff4928ffe907
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510797Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823184}

chrome/browser/sync/test/integration/configuration_refresher.cc

@@ -20,3 +20,7 @@ void ConfigurationRefresher::OnSyncConfigurationCompleted(
   sync_service->TriggerRefresh(syncer::Intersection(
       sync_service->GetActiveDataTypes(), syncer::ProtocolTypes()));
 }
+
+void ConfigurationRefresher::OnSyncShutdown(syncer::SyncService* sync_service) {
+  scoped_observer_.Remove(sync_service);
+}

chrome/browser/sync/test/integration/configuration_refresher.h

@@ -27,6 +27,7 @@ class ConfigurationRefresher : public syncer::SyncServiceObserver {
  private:
   // syncer::SyncServiceObserver implementation.
   void OnSyncConfigurationCompleted(syncer::SyncService* sync_service) override;
+  void OnSyncShutdown(syncer::SyncService* sync_service) override;
 
   ScopedObserver<syncer::SyncService, syncer::SyncServiceObserver>
       scoped_observer_{this};