Add css-will-change-1.vim and test

See Also: http://www.w3.org/TR/2014/WD-css-will-change-1-20140429/

test/test.css

@@ -551,6 +551,10 @@
   var-foo: var(foo);
 }
 
+.will-change {
+  will-change: scroll-position;
+}
+
 .writing-modes {
   text-orientation: before;
   text-combine-horizontal: after;

test/test.html

@@ -559,6 +559,10 @@
         var-foo: var(foo);
       }
 
+      .will-change {
+        will-change: scroll-position;
+      }
+
       .writing-modes {
         text-orientation: before;
         text-combine-horizontal: after;