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

tracing/tracing/base/rect.html

Index: tracing/tracing/base/rect.html
diff --git a/tracing/tracing/base/rect.html b/tracing/tracing/base/rect.html
index 1ceb39933bcdffb7a2776a3276a60e2132ec9541..450de0a6fb9247a754686e0edb89636979cbe67c 100644
--- a/tracing/tracing/base/rect.html
+++ b/tracing/tracing/base/rect.html
@@ -31,8 +31,9 @@ tr.exportTo('tr.b', function() {
   };
 
   Rect.fromArray = function(ary) {
-    if (ary.length !== 4)
+    if (ary.length !== 4) {
       throw new Error('ary.length must be 4');
+    }
     var rect = new Rect();
     rect.x = ary[0];
     rect.y = ary[1];