[MD settings] keep radio button circles circular

chrome/browser/resources/settings/settings_shared_css.html

 <link rel="import" href="chrome://resources/cr_elements/shared_style_css.html">
 <link rel="import" href="settings_vars_css.html">
 
 <!-- Common styles for Material Design settings. -->
 <dom-module id="settings-shared">
   <template>
     <style include="cr-shared-style">
       /* Included here so we don't have to include "iron-positioning" in every
        * stylesheet. See crbug.com/498405. */
       [hidden] {
@@ skipping 117 matching lines @@
         --paper-checkbox-checked-color: var(--google-blue-500);
         --paper-checkbox-label-spacing: var(--settings-control-spacing);
         --paper-checkbox-size: var(--checkbox-size);
         --paper-checkbox-unchecked-color: var(--paper-grey-600);
         -webkit-margin-start: var(--checkbox-margin-start);
       }
 
       paper-radio-button {
         --paper-radio-button-checked-color: var(--google-blue-500);
         --paper-radio-button-label-spacing: 22px;
+        --paper-radio-button-radio-container: {
+          flex-shrink: 0;
+        };
         --paper-radio-button-unchecked-color: var(--paper-grey-600);
         -webkit-margin-start: 2px;
         align-items: center;
         display: flex;
         min-height: var(--settings-row-min-height);
       }
 
       paper-radio-group {
         width: 100%;
       }
@@ skipping 240 matching lines @@
         transform: rotate(-135deg);
       }
 
       .column-header {
         color: var(--paper-grey-600);
         font-weight: 500;
       }
     </style>
   </template>
 </dom-module>