Add getPropertyNames to v8 Dictionaries and make use of in Keyframes processing.

LayoutTests/web-animations-api/w3c/keyframe-properties.html

Index: LayoutTests/web-animations-api/w3c/keyframe-properties.html
diff --git a/LayoutTests/web-animations-api/w3c/keyframe-properties.html b/LayoutTests/web-animations-api/w3c/keyframe-properties.html
index 639151c95218da8253a6fe4812dddc2e33bf20e1..10a21950ab2bc8bea6246c233af36d79049cd735 100644
--- a/LayoutTests/web-animations-api/w3c/keyframe-properties.html
+++ b/LayoutTests/web-animations-api/w3c/keyframe-properties.html
@@ -36,11 +36,10 @@ test(function() {
     value: '100px',
     enumerable: 'true'});
   var keyframe = new Keyframe();
-  assert_array_equals(Object.keys(keyframe), ["top"]);
   try {
-    div.animate([keyframe, {top: '200px'}], 1);
+    div.animate([keyframe, {top: '200px', left: '200px', height: '200px'}], 1);
   } catch (e) {
-    assert_unreached("Mismatched properties - left, width or height considered on keyframe.");
+    assert_unreached("Mismatched properties - left, width or height not considered on keyframe.");
   }
 },
 'inherited keyframe properties tests',