[MD settings] mirror subpage back arrow in rtl

chrome/browser/resources/settings/settings_shared_css.html

Index: chrome/browser/resources/settings/settings_shared_css.html
diff --git a/chrome/browser/resources/settings/settings_shared_css.html b/chrome/browser/resources/settings/settings_shared_css.html
index 545e4f0f1e5e1ca2f001df798d06b57e671ccba3..65939c12ac805c4800df4892e236d50c9679f5c9 100644
--- a/chrome/browser/resources/settings/settings_shared_css.html
+++ b/chrome/browser/resources/settings/settings_shared_css.html
@@ -28,6 +28,10 @@
         background-image: url(images/open_in_new.svg);
       }
 
+      :host-context([dir=rtl]) paper-icon-button[icon='settings:arrow-back'] {
+        transform: scaleX(-1);  /* Flip on the X axis (aka mirror). */
+      }
+
       /* Use <h2> as the "sub-header" mentioned in the UX design docs. */
       h2 {
         align-items: center;