Fix all remaining print preview closure compiler errors

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

Index: chrome/browser/resources/print_preview/previewarea/margin_control.js
diff --git a/chrome/browser/resources/print_preview/previewarea/margin_control.js b/chrome/browser/resources/print_preview/previewarea/margin_control.js
index 07d2dcc6ad8f75d7a99a814c7cfd5e231d8906a1..d81c74242fcf133dc650e318f48368133e4e2d63 100644
--- a/chrome/browser/resources/print_preview/previewarea/margin_control.js
+++ b/chrome/browser/resources/print_preview/previewarea/margin_control.js
@@ -99,7 +99,7 @@ cr.define('print_preview', function() {
      * @private
      */
     this.isInError_ = false;
-  };
+  }
 
   /**
    * Event types dispatched by the margin control.
@@ -327,13 +327,15 @@ cr.define('print_preview', function() {
           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 */