[MD Settings] Add title to show/hide password button.

chrome/browser/resources/settings/passwords_and_forms_page/password_edit_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-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="../icons.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <dom-module id="password-edit-dialog">
   <template>
@@ skipping 20 matching lines @@
         <paper-input id="usernameInput" label="$i18n{editPasswordUsernameLabel}"
             value="[[item.loginPair.username]]" readonly>
         </paper-input>
         <div id="passwordGroup">
           <paper-input id="passwordInput"
               label="$i18n{editPasswordPasswordLabel}"
               type="[[getPasswordInputType_(password)]]"
               value="[[getPassword_(item, password)]]" readonly>
           </paper-input>
           <paper-icon-button id="showPasswordButton"
-              icon="settings:visibility" on-tap="onShowPasswordButtonTap_">
+              icon="settings:visibility" on-tap="onShowPasswordButtonTap_"
+              title="[[showPasswordTitle_(password,
+                  '$i18nPolymer{hidePassword}','$i18nPolymer{showPassword}')]]">
           </paper-icon-button>
         </div>
       </div>
       <div class="button-container">
         <paper-button id="cancelButton" class="cancel-button"
             on-tap="onCancelButtonTap_">$i18n{passwordsDone}</paper-button>
       </div>
     </dialog>
   </template>
   <script src="password_edit_dialog.js"></script>
 </dom-module>