MD Settings: Stop calling chrome.settingsPrivate.setDefaultZoomLevel on startup.

chrome/browser/resources/settings/appearance_page/appearance_page.js

 // Copyright 2015 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.
 
 /**
  * 'settings-appearance-page' is the settings page containing appearance
  * settings.
  *
  * Example:
  *
@@ skipping 31 matching lines @@
 
     /**
      * @private
      */
     defaultZoomLevel_: {
       notify: true,
       type: Object,
       value: function() {
         return {
           type: chrome.settingsPrivate.PrefType.NUMBER,
+          /* Needed such that the pref can be initialized without unnecessarily
+           * invoking chrome.settingsPrivate.setDefaultZoomPercent(). */
+          initialized: false,

[michaelpg, 2016/10/11 03:47:33]

We probably shouldn't "overload" this value more than we already do -- it'd be a
partial PrefObject with an extra |initialized| member. How about a separate
defaultZoomLevelInitialized_ property?

[dpapad, 2016/10/11 17:30:17]

Done.

         };
       },
     },
 
     /**
      * List of options for the font size drop-down menu.
      * @type {!DropdownMenuOptionList}
      */
     fontSizeOptions_: {
       readOnly: true,
@@ skipping 144 matching lines @@
   },
 
   /**
    * @param {number} percent The integer percentage of the page zoom.
    * @private
    */
   zoomLevelChanged_: function(percent) {
     // The |percent| may be undefined on startup.
     if (percent === undefined)
       return;
+
+    if (!this.defaultZoomLevel_.initialized) {

[michaelpg, 2016/10/11 03:47:33]

Since we only use this here, I wouldn't be averse to just defining it here (and
nowhere else) rather than making it part of a "type".

[dpapad, 2016/10/11 17:30:17]

What do you mean defining it only here? Here in this scope? Needs to be
persisted across different calls of  zoomLevelChanged.

[michaelpg, 2016/10/11 22:01:10]

Oh, I was just saying, this is JS, we don't have to declare all our properties.
So using this.defaultZLI_ *only* in this function is OK:

if (!this.defaultZoomLevelInitialized_) {
  // Simply mark this pref as initialized, etc....
  /** @private */this.defaultZoomLevelInitialized_ = true;
  return;
}

as a plus, you don't need the 6-line comment in the latest patch.

[dpapad, 2016/10/11 22:05:54]

Ah, got it now. Personally I don't prefer augmenting properties to an object
outside the constructor. JS Compiler enforces this if @struct is used (which I
know we are not using), but nonetheless just feels wrong. I am fine with
declaring it with @private {boolean} before using it here.

+      // Simply mark this pref as initialized, no actual change was requested by
+      // the user.
+      this.defaultZoomLevel_.initialized = true;
+      return;
+    }
+
     chrome.settingsPrivate.setDefaultZoomPercent(percent);
   },
 
   /**
    * @param {boolean} bookmarksBarVisible if bookmarks bar option is visible.
    * @return {string} 'first' if the argument is false or empty otherwise.
    * @private
    */
   getFirst_: function(bookmarksBarVisible) {
     return !bookmarksBarVisible ? 'first' : '';
   }
 });