Fix crash on chrome://sync-internals when sync is disabled.

BUG=

Review URL: https://codereview.chromium.org/537893002

Cr-Commit-Position: refs/heads/master@{#293330}

chrome/browser/ui/webui/sync_internals_message_handler.cc

@@ -95,8 +95,8 @@ void SyncInternalsMessageHandler::HandleRegisterForPerTypeCounters(
     const base::ListValue* args) {
   DCHECK(args->empty());
 
-  ProfileSyncService* service = GetProfileSyncService();
-  if (service && !is_registered_for_counters_) {
+  if (ProfileSyncService* service = GetProfileSyncService()) {
+    if (!is_registered_for_counters_) {
       service->AddTypeDebugInfoObserver(this);
       is_registered_for_counters_ = true;
     } else {
@@ -104,6 +104,7 @@ void SyncInternalsMessageHandler::HandleRegisterForPerTypeCounters(
       service->RemoveTypeDebugInfoObserver(this);
       service->AddTypeDebugInfoObserver(this);
     }
+  }
 }
 
 void SyncInternalsMessageHandler::HandleRequestUpdatedAboutInfo(