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

chrome/browser/resources/settings/downloads_page/downloads_browser_proxy.js

Index: chrome/browser/resources/settings/downloads_page/downloads_browser_proxy.js
diff --git a/chrome/browser/resources/settings/downloads_page/downloads_browser_proxy.js b/chrome/browser/resources/settings/downloads_page/downloads_browser_proxy.js
index 2f510a1d012f9189d4baf484246263934d97b612..88c41dbafbc73527e01bb8380d831434655310bb 100644
--- a/chrome/browser/resources/settings/downloads_page/downloads_browser_proxy.js
+++ b/chrome/browser/resources/settings/downloads_page/downloads_browser_proxy.js
@@ -4,40 +4,33 @@
 
 cr.define('settings', function() {
   /** @interface */
-  function DownloadsBrowserProxy() {}
-
-  DownloadsBrowserProxy.prototype = {
-    initializeDownloads: assertNotReached,
-
-    selectDownloadLocation: assertNotReached,
-
-    resetAutoOpenFileTypes: assertNotReached,
-  };
+  class DownloadsBrowserProxy {
+    initializeDownloads() {}
+    selectDownloadLocation() {}
+    resetAutoOpenFileTypes() {}
+  }
 
   /**
    * @implements {settings.DownloadsBrowserProxy}
-   * @constructor
    */
-  function DownloadsBrowserProxyImpl() {}
-
-  cr.addSingletonGetter(DownloadsBrowserProxyImpl);
-
-  DownloadsBrowserProxyImpl.prototype = {
+  class DownloadsBrowserProxyImpl {
     /** @override */
-    initializeDownloads: function() {
+    initializeDownloads() {
       chrome.send('initializeDownloads');
-    },
+    }
 
     /** @override */
-    selectDownloadLocation: function() {
+    selectDownloadLocation() {
       chrome.send('selectDownloadLocation');
-    },
+    }
 
     /** @override */
-    resetAutoOpenFileTypes: function() {
+    resetAutoOpenFileTypes() {
       chrome.send('resetAutoOpenFileTypes');
-    },
-  };
+    }
+  }
+
+  cr.addSingletonGetter(DownloadsBrowserProxyImpl);
 
   return {
     DownloadsBrowserProxy: DownloadsBrowserProxy,