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

chrome/browser/resources/settings/appearance_page/appearance_fonts_page.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="fonts_browser_proxy.html">
 <link rel="import" href="../controls/settings_slider.html">
 <link rel="import" href="../controls/settings_dropdown_menu.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="../settings_shared_css.html">
 
@@ skipping 93 matching lines @@
     </div>
     <div class="list-frame">
       <div class="list-item">
         <settings-dropdown-menu class="start" label="$i18n{fixedWidthFont}"
             pref="{{prefs.webkit.webprefs.fonts.fixed.Zyyy}}"
             menu-options="[[fontOptions_]]">
         </settings-dropdown-menu>
       </div>
       <div class="list-item"
           style="
-              font-size:[[prefs.webkit.webprefs.default_font_size.value]]px;
+              font-size:
+                  [[prefs.webkit.webprefs.default_fixed_font_size.value]]px;

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

This is part of the 'also fixed' an not the primary fix in this CL. This wasn't
actually showing the example in the correct font size.

               font-family:
                   '[[prefs.webkit.webprefs.fonts.fixed.Zyyy.value]]';">
-        <span>
-          [[prefs.webkit.webprefs.default_font_size.value]]:
-          $i18n{quickBrownFox}
-        </span>
+        $i18n{quickBrownFox}

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

So it looks strange to show that this is 3px smaller than the others. I looked
to see what was done previously and the font size is simply not shown for the
fixed font size, which is less distracting.

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

SGTM. It would be more consistent to remove the prefixes on the other samples,
too, but we'd need to show it somewhere (the font size row, maybe?) and that's a
whole 'nother UX decision.

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

Acknowledged.

       </div>
     </div>
     <template is="dom-if" if="[[!isGuest_]]">
       <div class="settings-box two-line" id="advancedButton"
           on-tap="openAdvancedExtension_" actionable>
         <div class="start">
           $i18n{advancedFontSettings}
           <div class="secondary" id="advancedButtonSublabel">
             [[advancedExtensionSublabel_]]
           </div>
         </div>
         <button class="icon-external" is="paper-icon-button-light"
             aria-label="$i18n{advancedFontSettings}"
             aria-describedby="advancedButtonSublabel"></button>
       </div>
     </template>
   </template>
   <script src="appearance_fonts_page.js"></script>
 </dom-module>