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

tracing/tracing/model/stack_frame.html

Index: tracing/tracing/model/stack_frame.html
diff --git a/tracing/tracing/model/stack_frame.html b/tracing/tracing/model/stack_frame.html
index 67b378577edfb127372a5e542387989d3ccc9a35..a9cf23c089fb4d97cbded3ab1ec3d21d7f644462 100644
--- a/tracing/tracing/model/stack_frame.html
+++ b/tracing/tracing/model/stack_frame.html
@@ -10,8 +10,9 @@ found in the LICENSE file.
 
 tr.exportTo('tr.model', function() {
   function StackFrame(parentFrame, id, title, colorId, opt_sourceInfo) {
-    if (id === undefined)
+    if (id === undefined) {
       throw new Error('id must be given');
+    }
     this.parentFrame_ = parentFrame;
     this.id = id;
     this.title_ = title;
@@ -19,8 +20,9 @@ tr.exportTo('tr.model', function() {
     this.children = [];
     this.sourceInfo_ = opt_sourceInfo;
 
-    if (this.parentFrame_)
+    if (this.parentFrame_) {
       this.parentFrame_.addChild(this);
+    }
   }
 
   StackFrame.prototype = {
@@ -42,10 +44,12 @@ tr.exportTo('tr.model', function() {
      */
     get domain() {
       var result = 'unknown';
-      if (this.sourceInfo_ && this.sourceInfo_.domain)
+      if (this.sourceInfo_ && this.sourceInfo_.domain) {
         result = this.sourceInfo_.domain;
-      if (result === 'unknown' && this.parentFrame)
+      }
+      if (result === 'unknown' && this.parentFrame) {
         result = this.parentFrame.domain;
+      }
       return result;
     },
 
@@ -54,11 +58,13 @@ tr.exportTo('tr.model', function() {
     },
 
     set parentFrame(parentFrame) {
-      if (this.parentFrame_)
+      if (this.parentFrame_) {
         Polymer.dom(this.parentFrame_).removeChild(this);
+      }
       this.parentFrame_ = parentFrame;
-      if (this.parentFrame_)
+      if (this.parentFrame_) {
         this.parentFrame_.addChild(this);
+      }
     },
 
     addChild: function(child) {
@@ -67,14 +73,16 @@ tr.exportTo('tr.model', function() {
 
     removeChild: function(child) {
       var i = this.children.indexOf(child.id);
-      if (i === -1)
+      if (i === -1) {
         throw new Error('omg');
+      }
       this.children.splice(i, 1);
     },
 
     removeAllChildren: function() {
-      for (var i = 0; i < this.children.length; i++)
+      for (var i = 0; i < this.children.length; i++) {
         this.children[i].parentFrame_ = undefined;
+      }
       this.children.splice(0, this.children.length);
     },