MD Settings: more consistently fix error message space for search engine

chrome/browser/resources/settings/search_engines_page/search_engine_dialog.html

 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_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-input/paper-input.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="search_engines_browser_proxy.html">
 
 <dom-module id="settings-search-engine-dialog">
   <template>
     <style include="settings-shared">
       :host {
         --paper-input-container: {
           /**
            * Saves space for error message. Using calc to leave just enough
            * space at all font sizes (default 0, grow/shrink with font-size).
+           * Using padding instead of padding-bottom to prevent 
+           * paper-input-container's default padding rule to eat up the
+           * padding-bottom rule.
            */
-          padding-bottom: calc(1rem - 8px);
+          padding: 8px 0 calc(1rem - 8px) 0;
         };
       }
     </style>
     <dialog is="cr-dialog" id="dialog" close-text="$i18n{close}">
       <div class="title">[[dialogTitle_]]</div>
       <div class="body" on-keypress="onKeypress_">
         <paper-input always-float-label id="searchEngine"
             label="$i18n{searchEnginesSearchEngine}"
             error-message="$i18n{notValid}"
             value="{{searchEngine_}}" on-input="validate_"
@@ skipping 16 matching lines @@
             $i18n{cancel}</paper-button>
         <paper-button id="actionButton" class="action-button"
             on-tap="onActionButtonTap_">
           [[actionButtonText_]]
         </paper-button>
       </div>
     </dialog>
   </template>
   <script src="search_engine_dialog.js"></script>
 </dom-module>