MD Settings: Convert all browser proxies to use ES6 class syntax.

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

 // Copyright 2016 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.
 
 /**
  * @typedef {{
  *   fontList: Array<{0: string, 1: (string|undefined), 2: (string|undefined)}>,
  *   extensionUrl: string
  * }}
  */
 var FontsData;
 
 cr.define('settings', function() {
   /** @interface */
-  function FontsBrowserProxy() {}
-
-  FontsBrowserProxy.prototype = {
+  class FontsBrowserProxy {
     /**
      * @return {!Promise<!FontsData>} Fonts and the advanced font settings
      *     extension URL.
      */
-    fetchFontsData: assertNotReached,
+    fetchFontsData() {}
 
-    observeAdvancedFontExtensionAvailable: assertNotReached,
+    observeAdvancedFontExtensionAvailable() {}
 
-    openAdvancedFontSettings: assertNotReached,

[scottchen, 2017/06/27 21:14:10]

for future readers:
Had a discussion with @dpapad about assertNotReached logic being removed, and
concluded that we didn't need it originally anyway, because the implementations
wasn't doing actual sub-classing, so the methods were not gonna fall through
anyway.

-  };
+    openAdvancedFontSettings() {}
+  }
 
   /**
    * @implements {settings.FontsBrowserProxy}
-   * @constructor
    */
-  function FontsBrowserProxyImpl() {}
+  class FontsBrowserProxyImpl {
+    /** @override */
+    fetchFontsData() {
+      return cr.sendWithPromise('fetchFontsData');
+    }
+
+    /** @override */
+    observeAdvancedFontExtensionAvailable() {
+      chrome.send('observeAdvancedFontExtensionAvailable');
+    }
+
+    /** @override */
+    openAdvancedFontSettings() {
+      chrome.send('openAdvancedFontSettings');
+    }
+  }
 
   cr.addSingletonGetter(FontsBrowserProxyImpl);
 
-  FontsBrowserProxyImpl.prototype = {
-    /** @override */
-    fetchFontsData: function() {
-      return cr.sendWithPromise('fetchFontsData');
-    },
-
-    /** @override */
-    observeAdvancedFontExtensionAvailable: function() {
-      chrome.send('observeAdvancedFontExtensionAvailable');
-    },
-
-    /** @override */
-    openAdvancedFontSettings: function() {
-      chrome.send('openAdvancedFontSettings');
-    }
-  };
-
   return {
     FontsBrowserProxy: FontsBrowserProxy,
     FontsBrowserProxyImpl: FontsBrowserProxyImpl,
   };
 });