[MD settings] CSS var --checkbox-spacing to --settings-control-spacing

chrome/browser/resources/settings/controls/controlled_radio_button.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-radio-button/paper-radio-button.html">
 <link rel="import" href="chrome://resources/cr_elements/policy/cr_policy_pref_indicator.html">
 <link rel="import" href="pref_control_behavior.html">
 <link rel="import" href="../prefs/pref_util.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <dom-module id="controlled-radio-button">
   <template>
     <style include="settings-shared">
       :host {
         align-items: center;
         display: flex;
         outline: none;
       }
 
       #radioButton {
         flex: 1;
       }
 
       :host([controlled_]) {
         /* Disable pointer events for this whole element, as outer on-tap gets
          * triggered when clicking/tapping anywhere in :host. */
         pointer-events: none;
       }
 
       cr-policy-pref-indicator {
-        -webkit-margin-start: var(--checkbox-spacing);
+        -webkit-margin-start: var(--settings-control-spacing);
         /* Enable pointer events for the indicator so :hover works. Disable
          * clicks/taps via onIndicatorTap_ so outer on-tap doesn't trigger. */
         pointer-events: all;
       }
     </style>
 
     <paper-radio-button id="radioButton" name="{{name}}" checked="{{checked}}"
         disabled="[[controlled_]]" tabindex$="[[tabindex]]">
       [[label]] <content></content>
     </paper-radio-button>
 
     <template is="dom-if" if="[[showIndicator_(controlled_, name, pref.*)]]">
       <cr-policy-pref-indicator pref="[[pref]]" on-tap="onIndicatorTap_"
           icon-aria-label="[[label]]">
       </cr-policy-pref-indicator>
     </template>
 
   </template>
   <script src="controlled_radio_button.js"></script>
 </dom-module>