[NTP] Fix spacing between cancel and done in edit shortcut dialog for RTL

Before: https://screenshot.googleplex.com/VTEZEnvP8Ac.png
After: https://screenshot.googleplex.com/QpJWqkymMe8.png

Bug: 879502
Change-Id: I4a37757b19297c3507b55d8506446dd1f58ecbc5
Reviewed-on: https://chromium-review.googlesource.com/1252854
Commit-Queue: Kristi Park <kristipark@chromium.org>
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595584}

chrome/browser/resources/local_ntp/custom_links_edit.css

@@ -192,6 +192,10 @@ button.secondary:active:not(:disabled) {
       0 3px 6px 2px rgba(60, 64, 67, 0.15);
 }
 
-#cancel {
+html:not([dir=rtl]) #cancel {
   margin-right: 8px;
 }
+
+html[dir=rtl] #cancel {
+  margin-left: 8px;
+}