MD Settings: Add "Auto Open" setting to Downloads page UI.

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

+// Copyright 2017 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.
+
+cr.define('settings', function() {
+  /** @interface */
+  function DownloadsBrowserProxy() {}
+
+  DownloadsBrowserProxy.prototype = {
+    initializeDownloads: assertNotReached,
+
+    selectDownloadLocation: assertNotReached,
+
+    resetAutoOpenFileTypes: assertNotReached,
+  };
+
+  /**
+   * @implements {settings.DownloadsBrowserProxy}
+   * @constructor
+   */
+  function DownloadsBrowserProxyImpl() {}
+
+  cr.addSingletonGetter(DownloadsBrowserProxyImpl);
+
+  DownloadsBrowserProxyImpl.prototype = {
+    /** @override */
+    initializeDownloads: function() {
+      chrome.send('initializeDownloads');
+    },
+
+    /** @override */
+    selectDownloadLocation: function() {
+      chrome.send('selectDownloadLocation');
+    },
+
+    /** @override */
+    resetAutoOpenFileTypes: function() {
+      chrome.send('resetAutoOpenFileTypes');
+    },
+  };
+
+  return {
+    DownloadsBrowserProxy: DownloadsBrowserProxy,
+    DownloadsBrowserProxyImpl: DownloadsBrowserProxyImpl,
+  };
+});