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

tracing/tracing/base/unit_scale.html

Index: tracing/tracing/base/unit_scale.html
diff --git a/tracing/tracing/base/unit_scale.html b/tracing/tracing/base/unit_scale.html
index 78eeaf46a1ac52f20c02d46fb15558bbcb653eb5..69f9a2d7fbbdfc49400defce87dcb02e932da829 100644
--- a/tracing/tracing/base/unit_scale.html
+++ b/tracing/tracing/base/unit_scale.html
@@ -24,8 +24,9 @@ tr.exportTo('tr.b', function() {
   var UnitScale = {};
 
   function defineUnitPrefixScale(name, prefixes) {
-    if (UnitPrefixScale[name] !== undefined)
+    if (UnitPrefixScale[name] !== undefined) {
       throw new Error('Unit prefix scale \'' + name + '\' already exists');
+    }
     if (prefixes.AUTO !== undefined) {
       throw new Error('The \'AUTO\' unit prefix is not supported for unit' +
           'prefix scales and cannot be added to scale \'' + name + '\'');
@@ -35,8 +36,9 @@ tr.exportTo('tr.b', function() {
   }
 
   UnitScale.defineUnitScale = function(name, unitScale) {
-    if (UnitScale[name] !== undefined)
+    if (UnitScale[name] !== undefined) {
       throw new Error('Unit scale \'' + name + '\' already exists');
+    }
     if (unitScale.AUTO !== undefined) {
       throw new Error('\'AUTO\' unit scale will be added automatically ' +
           'for unit scale \'' + name + '\'');