MD Settings: in spell-check page, disable add button when input is empty.

chrome/browser/resources/settings/languages_page/edit_dictionary_page.html

 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-a11y-keys/iron-a11y-keys.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.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-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <dom-module id="settings-edit-dictionary-page">
@@ skipping 21 matching lines @@
       }
 
       paper-button {
         -webkit-margin-start: 16px;
       }
     </style>
     <div class="settings-box first">
       <iron-a11y-keys id="keys" keys="enter esc"
           on-keys-pressed="onKeysPress_"></iron-a11y-keys>
       <div class="start">
-        <paper-input id="newWord" no-label-float
+        <paper-input id="newWord" no-label-float value="{{newWordValue_}}"
             label="$i18n{addDictionaryWordLabel}"></paper-input>
       </div>
-      <paper-button class="secondary-button" on-tap="onAddWordTap_">
+      <paper-button class="secondary-button" on-tap="onAddWordTap_"
+          disabled="[[!validateWord_(newWordValue_)]]">
         $i18n{addDictionaryWordButton}
       </paper-button>
     </div>
     <div class="settings-box continuation block">
       <h2>$i18n{customDictionaryWords}</h2>
       <div class="list-frame">
         <iron-list id="list" items="{{words_}}">
           <template>
             <div class="list-item">
               <div class="word text-elide">[[item]]</div>
               <paper-icon-button icon="cr:clear" on-tap="onRemoveWordTap_"
                   tabindex$="[[tabIndex]]">
               </paper-icon-button>
             </div>
           </template>
         </iron-list>
       </div>
     </div>
   </template>
   <script src="edit_dictionary_page.js"></script>
 </dom-module>