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

chrome/browser/resources/settings/downloads_page/downloads_page.html

Index: chrome/browser/resources/settings/downloads_page/downloads_page.html
diff --git a/chrome/browser/resources/settings/downloads_page/downloads_page.html b/chrome/browser/resources/settings/downloads_page/downloads_page.html
index 64af1e7a93b9f7e9c60d505dc199c1b2a5b38be8..f143211a747bc52efca01b31c4b9c71a4c691cc4 100644
--- a/chrome/browser/resources/settings/downloads_page/downloads_page.html
+++ b/chrome/browser/resources/settings/downloads_page/downloads_page.html
@@ -1,4 +1,5 @@
 <link rel="import" href="chrome://resources/html/polymer.html">
+<link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="../controls/controlled_button.html">
 <link rel="import" href="../controls/settings_toggle_button.html">
@@ -41,6 +42,17 @@
       </settings-toggle-button>
 </if>
     </div>
+    <div class="settings-box" hidden="[[!autoOpenDownloads_]]">

[Dan Beam, 2017/02/27 05:50:36]

can you make this a dom-if instead of binding to hidden?

[tommycli, 2017/02/28 00:47:26]

Done.

+      <div class="start">
+        $i18n{openFileTypesAutomatically}
+      </div>
+      <div class="secondary-action">
+        <paper-button on-tap="onClearAutoOpenFileTypesTap_"
+            class="secondary-button">
+          $i18n{clear}
+        </paper-button>
+      </div>
+    </div>
   </template>
   <script src="downloads_page.js"></script>
 </dom-module>