[ESLint] Fix violations when enabling curly rule in eslint.

tracing/tracing/ui/analysis/single_async_slice_sub_view.html

Index: tracing/tracing/ui/analysis/single_async_slice_sub_view.html
diff --git a/tracing/tracing/ui/analysis/single_async_slice_sub_view.html b/tracing/tracing/ui/analysis/single_async_slice_sub_view.html
index b2238040827d101d88ace9c706fad82318096483..b3e1ba49802378a508b801543c6f408cae3e98a4 100644
--- a/tracing/tracing/ui/analysis/single_async_slice_sub_view.html
+++ b/tracing/tracing/ui/analysis/single_async_slice_sub_view.html
@@ -40,8 +40,9 @@ Polymer({
   },
 
   set selection(selection) {
-    if (selection.length !== 1)
+    if (selection.length !== 1) {
       throw new Error('Only supports single slices');
+    }
     this.$.content.setSelectionWithoutErrorChecks(selection);
     this.$.relatedEvents.setRelatedEvents(selection);
     if (this.$.relatedEvents.hasRelatedEvents()) {
@@ -64,8 +65,7 @@ Polymer({
   },
 
   get relatedEventsToHighlight() {
-    if (!this.currentSelection_)
-      return undefined;
+    if (!this.currentSelection_) return undefined;
     return tr.b.getOnlyElement(this.currentSelection_).associatedEvents;
   }
 });