WebUI: Fix dialog showing unnecessary scrollbars

ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html

 <link rel="import" href="chrome://resources/cr_elements/hidden_style_css.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/assert.html">
 <link rel="import" href="chrome://resources/html/polymer.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-styles/default-theme.html">
 
 <dom-module id="cr-dialog">
   <template>
     <style include="cr-hidden-style">
       :host {
         --scroll-border: 1px solid var(--paper-grey-300);
         border: 0;
         border-radius: 2px;
         bottom: 0;
         box-shadow: 0 0 16px rgba(0, 0, 0, 0.12),
                     0 16px 16px rgba(0, 0, 0, 0.24);
         color: inherit;
-        overflow: scroll;
+        overflow: auto;
         padding: 0;
         top: 0;
         width: 512px;
       }
 
       :host([open]) {
         /* Keep max-height within viewport, and flex content accordingly. */
         display: flex;
         flex-direction: column;
         max-height: 100vh;
@@ skipping 109 matching lines @@
     <div class="body-container">
       <span id="bodyTopMarker"></span>
       <content select=".body"></content>
       <span id="bodyBottomMarker"></span>
     </div>
     <content select=".button-container"></content>
     <content select=".footer"></content>
   </template>
   <script src="cr_dialog.js"></script>
 </dom-module>