Navi: Flip chevron on NTP module for rtl languages

https://i.imgur.com/nDH165a.png

Change-Id: I19f7662098f6bee115b2b55f1e695875a5eda822
Reviewed-on: https://chromium-review.googlesource.com/c/1474843
Commit-Queue: John Lee <johntlee@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632759}

chrome/browser/resources/welcome/onboarding_welcome/ntp_background/nux_ntp_background.html

@@ -116,6 +116,10 @@
         margin-inline-start: 6px;
         width: 20px;
       }
+
+      :host-context([dir=rtl]) iron-icon {
+        transform: scaleX(-1);
+      }
     </style>
     <div class="ntp-background-logo"></div>
     <h1 tabindex="-1">$i18n{ntpBackgroundDescription}</h1>