[MD settings] hide scrollbar during animation to subpage

chrome/browser/resources/settings/basic_page/basic_page.html

Index: chrome/browser/resources/settings/basic_page/basic_page.html
diff --git a/chrome/browser/resources/settings/basic_page/basic_page.html b/chrome/browser/resources/settings/basic_page/basic_page.html
index 257bace768b0e61a28f220836e81db3f6857b11a..3a9bb9b94d8f01fc784838052f399e808a6fe7f3 100644
--- a/chrome/browser/resources/settings/basic_page/basic_page.html
+++ b/chrome/browser/resources/settings/basic_page/basic_page.html
@@ -28,6 +28,12 @@
 <dom-module id="settings-basic-page">
   <template>
     <style include="settings-page-styles">
+      :host([is-subpage-animating]) {
+        /* Prevent an unwanted horizontal scrollbar when transitioning back from
+         * a sub-page. */
+        overflow: hidden;
+      }
+
       #advancedToggle {
         --paper-button: {
           text-transform: none;