DevTools: Remove unused variables. Disallow unused variables with eslint

third_party/WebKit/Source/devtools/front_end/ui/Widget.js

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2011 Google Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 366 matching lines @@
       this._hideWidget(true);
 
     // Update widget hierarchy.
     if (this._parentWidget) {
       var childIndex = this._parentWidget._children.indexOf(this);
       UI.Widget.__assert(childIndex >= 0, 'Attempt to remove non-child widget');
       this._parentWidget._children.splice(childIndex, 1);
       if (this._parentWidget._defaultFocusedChild === this)
         this._parentWidget._defaultFocusedChild = null;
       this._parentWidget.childWasDetached(this);
-      var parent = this._parentWidget;
       this._parentWidget = null;
       this._processWasDetachedFromHierarchy();
     } else {
       UI.Widget.__assert(this._isRoot, 'Removing non-root widget from DOM');
     }
 
     this._attachedToParentElement = null;
     this._attachedBeforeNode = null;
   }
 
@@ skipping 359 matching lines @@
   UI.Widget.__assert(
       !child.__widgetCounter && !child.__widget,
       'Attempt to remove element containing widget via regular DOM operation');
   return UI.Widget._originalRemoveChild.call(this, child);
 };
 
 Element.prototype.removeChildren = function() {
   UI.Widget.__assert(!this.__widgetCounter, 'Attempt to remove element containing widget via regular DOM operation');
   UI.Widget._originalRemoveChildren.call(this);
 };