Fix all remaining print preview closure compiler errors

chrome/browser/resources/print_preview/previewarea/margin_control.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 cr.define('print_preview', function() {
   'use strict';
 
   /**
    * Draggable control for setting a page margin.
    * @param {!print_preview.ticket_items.CustomMarginsOrientation} orientation
@@ skipping 81 matching lines @@
      * @private
      */
     this.isFocused_ = false;
 
     /**
      * Whether the margin control is in an error state.
      * @type {boolean}
      * @private
      */
     this.isInError_ = false;
-  };
+  }
 
   /**
    * Event types dispatched by the margin control.
    * @enum {string}
    */
   MarginControl.EventType = {
     // Dispatched when the margin control starts dragging.
     DRAG_START: 'print_preview.MarginControl.DRAG_START',
 
     // Dispatched when the text in the margin control's textbox changes.
@@ skipping 207 matching lines @@
 
     /** @override */
     enterDocument: function() {
       print_preview.Component.prototype.enterDocument.call(this);
       this.tracker.add(
           this.getElement(), 'mousedown', this.onMouseDown_.bind(this));
       this.tracker.add(
           this.getElement(),
           'transitionend',
           this.onTransitionEnd_.bind(this));
+      assert(this.textbox_);
       this.tracker.add(
           this.textbox_, 'input', this.onTextboxInput_.bind(this));
       this.tracker.add(
           this.textbox_, 'keydown', this.onTextboxKeyDown_.bind(this));
       this.tracker.add(
           this.textbox_, 'focus', this.setIsFocused_.bind(this, true));
       this.tracker.add(this.textbox_, 'blur', this.onTexboxBlur_.bind(this));
     },
 
     /** @override */
@@ skipping 105 matching lines @@
       this.setIsFocused_(false);
       cr.dispatchSimpleEvent(this, MarginControl.EventType.TEXT_CHANGE);
     }
   };
 
   // Export
   return {
     MarginControl: MarginControl
   };
 });