Options (chrome://settings/fonts)

1. Change the standard (default) font size from 16 to 32.
2. Observe the fixed width font sample get larger.
3. Set the standard font size back to 16.
3. CLOSE ALL SETTINGS TABS.

MD Settings (chrome://md-settings -> Customize fonts):

1. Change the standard (default) font size from 16 to 32.
2. Observe the fixed width sample get larger.
3. Open Options again and open the Fonts dialog.

Expected: the fixed-width font is sample is large, like the other fonts.
Actual: the fixed-width font sample has not been updated.

MD Settings is "cheating" by using the default font size to display the fixed width font size, which is why this bug was hard to see. It shouldn't cheat, for the same reason.

The root of the bug: appearance_fonts_page.js sets 'prefs.webkit.webprefs.default_fixed_font_size.value', but since that pref is never actually fetched from C++, there is no Polymer path there, and the function does nothing.

The result is that the fixed font size is not updated when the default font size is updated.

You can verify this with:
chrome.settingsPrivate.getPref('webkit.webprefs.default_fixed_font_size', console.log.bind(console));

Note that Options must be closed for the bug to repro.