showw urlbar button: remove max-width from flexible spaces

This way they can grow to fill available width in the toolbar now that
urlbar can't do that.

chrome/show_urlbar_button.css

@@ -64,4 +64,8 @@ See the above repository for updates as well as full license text. */
 #urlbar-input:not(:focus-within){
   opacity: 0;
   cursor: default;
+}
+/* Make flexible spaces have unlimited width so that they can claim empty space that urlbar would normally claim */
+#nav-bar-customization-target > toolbarspring{
+  max-width: none !important;
 }