[MD settings] observe changes to default font size in Appearance

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.
 
+
+/**
+ * This is the absolute difference maintained between standard and
+ * fixed-width font sizes. http://crbug.com/91922.
+ * @const @private {number}
+ */
+var SIZE_DIFFERENCE_FIXED_STANDARD_ = 3;
+
+
 /**
  * 'settings-appearance-page' is the settings page containing appearance
  * settings.
  *
  * Example:
  *
  *    <iron-animated-pages>
  *      <settings-appearance-page prefs="{{prefs}}">
  *      </settings-appearance-page>
  *      ... other pages ...
@@ skipping 88 matching lines @@
     },
   },
 
   /** @private {?settings.AppearanceBrowserProxy} */
   browserProxy_: null,
 
   /** @private {string} */
   themeUrl_: '',
 
   observers: [
+    'onDefaultFontSizeChanged_(prefs.webkit.webprefs.default_font_size.value)',

[michaelpg, 2017/04/17 20:06:28]

nit: consistency w/ other observers: defaultFontSizeChanged_

[dschuyler, 2017/04/17 21:26:11]

Done.

     'themeChanged_(prefs.extensions.theme.id.value, useSystemTheme_)',
 
-// <if expr="is_linux and not chromeos">
+    // <if expr="is_linux and not chromeos">

[dschuyler, 2017/04/15 01:27:57]

This indention (here and below) is done by 
git cl format --js

     // NOTE: this pref only exists on Linux.
     'useSystemThemePrefChanged_(prefs.extensions.theme.use_system.value)',
-// </if>
+    // </if>
   ],
 
   created: function() {
     this.browserProxy_ = settings.AppearanceBrowserProxyImpl.getInstance();
   },
 
   ready: function() {
     this.$.defaultFontSize.menuOptions = this.fontSizeOptions_;
     // TODO(dschuyler): Look into adding a listener for the
     // default zoom percent.
@@ skipping 29 matching lines @@
   /** @private */
   onCustomizeFontsTap_: function() {
     settings.navigateTo(settings.Route.FONTS);
   },
 
   /** @private */
   onDisableExtension_: function() {
     this.fire('refresh-pref', 'homepage');
   },
 
+  /**
+   * @param {number} value The changed font size slider value.
+   * @private
+   */
+  onDefaultFontSizeChanged_: function(value) {
+    // This is unusual but there is a pref that is dependent upon another.

[michaelpg, 2017/04/17 20:06:28]

as a *minor* nit, could you try to condense this comment a bit?

[dschuyler, 2017/04/17 21:26:11]

Done.

+    // Whenever the |default_font_size| is changed, this will update the
+    // |default_fixed_font_size| as well. They can (and are) handled separately
+    // in extensions. In the built-in settings (here), they are tied together to
+    // simplify the UI.
+    this.set(
+        'prefs.webkit.webprefs.default_fixed_font_size.value',
+        value - SIZE_DIFFERENCE_FIXED_STANDARD_);
+  },
+
   /** @private */
   onThemesTap_: function() {
     window.open(this.themeUrl_ || loadTimeData.getString('themesGalleryUrl'));
   },
 
   // <if expr="chromeos">
   /**
    * ChromeOS only.
    * @private
    */
@@ skipping 65 matching lines @@
 
       this.browserProxy_.getThemeInfo(themeId).then(function(info) {
         this.themeSublabel_ = info.name;
       }.bind(this));
 
       this.themeUrl_ = 'https://chrome.google.com/webstore/detail/' + themeId;
       return;
     }
 
     var i18nId;
-// <if expr="is_linux and not chromeos">
+    // <if expr="is_linux and not chromeos">
     i18nId = useSystemTheme ? 'systemTheme' : 'classicTheme';
-// </if>
-// <if expr="not is_linux or chromeos">
+    // </if>
+    // <if expr="not is_linux or chromeos">
     i18nId = 'chooseFromWebStore';
-// </if>
+    // </if>
     this.themeSublabel_ = this.i18n(i18nId);
     this.themeUrl_ = '';
   },
 
   /** @private */
   onZoomLevelChange_: function() {
     chrome.settingsPrivate.setDefaultZoom(parseFloat(this.$.zoomLevel.value));
   },
 
   /**
    * @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' : '';
   },
 
   /**
    * @see content::ZoomValuesEqual().
    * @param {number} zoom1
    * @param {number} zoom2
    * @return {boolean}
    * @private
    */
   zoomValuesEqual_: function(zoom1, zoom2) {
     return Math.abs(zoom1 - zoom2) <= 0.001;
   },
 });