Add an initial implementation of the downloads MD settings page.

chrome/browser/resources/settings/prefs/prefs.js

Index: chrome/browser/resources/settings/prefs/prefs.js
diff --git a/chrome/browser/resources/settings/prefs/prefs.js b/chrome/browser/resources/settings/prefs/prefs.js
index a50dd7f9852e8b54892725b0cae13f7d54a66405..a13e03bb51337ba72f621648fa9bbaba0212be2a 100644
--- a/chrome/browser/resources/settings/prefs/prefs.js
+++ b/chrome/browser/resources/settings/prefs/prefs.js
@@ -34,6 +34,7 @@ Polymer('cr-settings-prefs', {
 
     this.settings = {};
     this.initializeA11y_();
+    this.initializeDownloads_();
     var observer = new ObjectObserver(this.settings);
     observer.open(this.propertyChangeCallback_.bind(this, 'settings'));
 
@@ -76,6 +77,17 @@ Polymer('cr-settings-prefs', {
   },
 
   /**
+   * Initializes some defaults for the downloads settings.
+   * @private
+   */
+  initializeDownloads_: function() {
+    this.settings.download = {
+      downloadLocation: '',
+      promptForDownload: false,
+    };
+  },
+
+  /**
    * @param {string} propertyPath The path before the property names.
    * @param {!Array<string>} added An array of keys which were added.
    * @param {!Array<string>} removed An array of keys which were removed.