Center the focus of the text input in magnifier screen.

chrome/browser/resources/options/browser_options.html

 <div id="settings" class="page" hidden>
   <header>
     <h1 i18n-content="settingsTitle"></h1>
   </header>
   <include src="reset_profile_settings_banner.html">
   <include src="automatic_settings_reset_banner.html">
 <if expr="chromeos">
   <link rel="import" href="chrome://resources/cr_elements/cr_network_icon/cr_network_icon.html">
   <link rel="import" href="chrome://resources/cr_elements/cr_onc/cr_onc_data.html">
   <include src="secondary_user_banner.html">
@@ skipping 867 matching lines @@
         <div id="accessibility-settings" hidden>
           <button id="accessibility-settings-button"
             i18n-content="accessibilitySettings"></button>
         </div>
       </div>
     </div>
     <div class="option-name">
       <div class="checkbox controlled-setting-with-label">
         <label>
           <input
+              id="accessibility-screen-magnifier-check"
               pref="settings.a11y.screen_magnifier" type="checkbox"
               metric="Options_AccessibilityScreenMagnifier">
           <span>
             <span i18n-content="accessibilityScreenMagnifier"></span>
             <span class="controlled-setting-indicator"
                 pref="settings.a11y.screen_magnifier"></span>
           </span>
         </label>
       </div>
+      <div class="checkbox controlled-setting-with-label">
+        <!-- No whitespace between elements. -->
+        <input type="checkbox" class="spacer-checkbox">
+        <label>
+          <input
+              id = "accessibility-screen-magnifier-center-focus-check"
+              pref="settings.a11y.screen_magnifier_center_focus" type="checkbox"
+              metric="Options_AccessibilityScreenMagnifierCenterFocus">
+          <span>
+            <span i18n-content="accessibilityScreenMagnifierCenterFocus"></span>
+            <span class="controlled-setting-indicator"
+                pref="settings.a11y.screen_magnifier_center_focus"></span>
+          </span>
+        </label>
+      </div>
     </div>
     <div class="option-name" id="accessibility-tap-dragging">
       <div class="checkbox">
         <label>
           <input id="accessibility-tap-dragging-check"
               pref="settings.touchpad.enable_tap_dragging" type="checkbox"
               metric="Options_AccessibilityTapDragging">
           <span i18n-content="accessibilityTapDragging"></span>
         </label>
       </div>
@@ skipping 100 matching lines @@
       </button>
     </div>
   </section>
   </div>  <!-- advanced-settings-container -->
   </div>  <!-- advanced-settings -->
   <footer id="advanced-settings-footer">
     <a is="action-link" id="advanced-settings-expander"
         i18n-content="showAdvancedSettings"></a>
   </footer>
 </div>