Add a collapsible toggle button to the MD "Passwords and Forms" section.

The toggle buttons are enabled/disabled based on the appropriate
setting. The buttons currently toggle properties that will control the
collapsible sections. The collapsible sections will be added in
follow-up CLs.

BUG=546836

Review URL: https://codereview.chromium.org/1474473003

Cr-Commit-Position: refs/heads/master@{#361399}

chrome/browser/resources/settings/passwords_and_forms_page/passwords_and_forms_page.html

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/polymer.html">
+<link rel="import" href="chrome://resources/cr_elements/cr_expand_button/cr_expand_button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-item/paper-item-body.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-item/paper-item.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-toggle-button/paper-toggle-button.html">
@@ -16,6 +17,8 @@
         <paper-toggle-button
             checked="{{prefs.autofill.enabled.value}}">
         </paper-toggle-button>
+        <cr-expand-button disabled="{{!prefs.autofill.enabled.value}}">
+        </cr-expand-button>
       </paper-item>
     </div>
     <div class="settings-box">
@@ -27,6 +30,9 @@
         <paper-toggle-button
             checked="{{prefs.profile.password_manager_enabled.value}}">
         </paper-toggle-button>
+        <cr-expand-button
+            disabled="{{!prefs.profile.password_manager_enabled.value}}">
+        </cr-expand-button>
       </paper-item>
     </div>
   </template>

chrome/browser/resources/settings/passwords_and_forms_page/passwords_and_forms_page.js

@@ -14,5 +14,15 @@
 
 Polymer({
   is: 'settings-passwords-and-forms-page',
+
+  properties: {
+    /**
+     * Preferences state.
+     */
+    prefs: {
+      type: Object,
+      notify: true,
+    },
+  },
 });
 })();