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));
-      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));
+      if (this.textbox_) {

[dpapad, 2017/05/08 20:40:10]

The previous code assumed that this.textbox_ was always populated by the time
this function executes, and if not, an error would be thrown in the console,
probably from [1]. The new code would silently do nothing, instead of letting
the code blow up to surface the programmer's error.

Can we assert() instead of using the if (..) check, to keep previous and new
code equivalent?
 

[1]
https://cs.chromium.org/chromium/src/ui/webui/resources/js/event_tracker.js?l=57

[rbpotter, 2017/05/08 23:28:20]

Done.

+        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 */
     exitDocument: function() {
       print_preview.Component.prototype.exitDocument.call(this);
       this.textbox_ = null;
       this.marginLineEl_ = null;
     },
 
     /**
@@ skipping 98 matching lines @@
       this.setIsFocused_(false);
       cr.dispatchSimpleEvent(this, MarginControl.EventType.TEXT_CHANGE);
     }
   };
 
   // Export
   return {
     MarginControl: MarginControl
   };
 });