[trace viewer] Fix bug where you can't close the help dialog >1 time

tracing/tracing/ui/base/overlay.html

Index: tracing/tracing/ui/base/overlay.html
diff --git a/tracing/tracing/ui/base/overlay.html b/tracing/tracing/ui/base/overlay.html
index df8e13ceddf7ee9e3377cb70678bf489c83518b1..e594ada82d9f05f0fbd22011195e0c5df399677f 100644
--- a/tracing/tracing/ui/base/overlay.html
+++ b/tracing/tracing/ui/base/overlay.html
@@ -5,8 +5,8 @@ Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
-<link rel="import" href="/tracing/base/utils.html">
 <link rel="import" href="/tracing/base/event.html">
+<link rel="import" href="/tracing/base/utils.html">
 <link rel="import" href="/tracing/ui/base/ui.html">
 <link rel="import" href="/tracing/ui/base/utils.html">
 
@@ -166,7 +166,6 @@ tr.exportTo('tr.ui.b', function() {
                                                         THIS_DOC));
 
       this.closeBtn_ = this.shadow_.querySelector('close-button');
-      this.closeBtn_.addEventListener('click', this.onClose_);
 
       this.shadow_
           .querySelector('overlay-frame')
@@ -223,6 +222,7 @@ tr.exportTo('tr.ui.b', function() {
       if (this.userCanClose_) {
         this.addEventListener('keydown', this.onKeyDown_.bind(this));
         this.addEventListener('click', this.onDocumentClick_.bind(this));
+        this.closeBtn_.addEventListener('click', this.onClose_);
       }
 
       this.parentEl_.addEventListener('focusin', this.onFocusIn_);
@@ -331,7 +331,7 @@ tr.exportTo('tr.ui.b', function() {
     o.buttons.appendChild(b);
     o.visible = true;
     return o;
-  }
+  };
 
   return {
     Overlay: Overlay