MD Settings: Certificate manager, implement importing CA certificate.

chrome/browser/resources/settings/certificate_manager_page/ca_trust_edit_dialog.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-checkbox/paper-checkbox.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-spinner/paper-spinner.html">
 <link rel="import" href="chrome://md-settings/i18n_setup.html">
 <link rel="import" href="chrome://md-settings/settings_dialog.html">
 <link rel="import" href="chrome://md-settings/settings_shared_css.html">
 <link rel="import" href="chrome://md-settings/certificate_manager_page/certificates_browser_proxy.html">
 
 <dom-module id="settings-ca-trust-edit-dialog">
   <template>
     <style include="settings-shared">
       paper-checkbox {
         display: block;
+        margin: 15px 0;
       }
     </style>
 
     <settings-dialog id="dialog">
       <div class="title">$i18n{certificateManagerCaTrustEditDialogTitle}</div>
       <div class="body">
         <div>[[explanationText_]]</div>
         <div>$i18n{certificateManagerCaTrustEditDialogDescription}</div>
         <paper-checkbox id="ssl" checked="[[trustInfo_.ssl]]">
           $i18n{certificateManagerCaTrustEditDialogSsl}
@@ skipping 11 matching lines @@
           $i18n{cancel}
         </paper-button>
         <paper-button id="ok" class="action-button" on-tap="onOkTap_">
           $i18n{ok}
         </paper-button>
       </div>
     </settings-dialog>
   </template>
   <script src="ca_trust_edit_dialog.js"></script>
 </dom-module>