Add css-contain-1.vim

See also: http://www.w3.org/TR/2017/WD-css-contain-1-20170221/

test/test.css

@@ -135,6 +135,12 @@
   display: luminosity;
 }
 
+.contain-1 {
+  contain: layout;
+  display: paint;
+  display: size;
+}
+
 .content-3 {
   string-set: open;
   bookmark-level: closed;

test/test.html

@@ -157,6 +157,13 @@
 }
 </style>
 <style>
+.contain-1 {
+  contain: layout;
+  display: paint;
+  display: size;
+}
+</style>
+<style>
 .content-3 {
   string-set: open;
   bookmark-level: closed;