[CSS Typed OM] Refactor is2D handling in CSSTransformComponents to match new spec

third_party/WebKit/LayoutTests/typedcssom/cssPerspective.html

Index: third_party/WebKit/LayoutTests/typedcssom/cssPerspective.html
diff --git a/third_party/WebKit/LayoutTests/typedcssom/cssPerspective.html b/third_party/WebKit/LayoutTests/typedcssom/cssPerspective.html
index 297762f3d61ab96c7e90e76580591d7931681463..faf45acb4493e64975ed331bb1123d135bf97906 100644
--- a/third_party/WebKit/LayoutTests/typedcssom/cssPerspective.html
+++ b/third_party/WebKit/LayoutTests/typedcssom/cssPerspective.html
@@ -33,5 +33,13 @@ test(() => {
   assert_equals(perspective.toString(), 'perspective(10px)');
 }, "toString should return perspective(<CSSNumericValue.cssString()>)");
 
+test(() => {
+  let perspective = new CSSPerspective(new CSSUnitValue(10, 'px'));
+  assert_false(perspective.is2D);
+
+  perspective.is2D = true;
+  assert_false(perspective.is2D);
+}, "Setting is2D does nothing");
+
 </script>