Remove property-specific handling in animation-test-helpers.js

LayoutTests/transitions/multiple-background-size-transitions.html

Index: LayoutTests/transitions/multiple-background-size-transitions.html
diff --git a/LayoutTests/transitions/multiple-background-size-transitions.html b/LayoutTests/transitions/multiple-background-size-transitions.html
index 92786c8dc970c458da11f045b0ab0794156baa00..0806be8298db76ebb63541feb8c8787bfe881a74 100644
--- a/LayoutTests/transitions/multiple-background-size-transitions.html
+++ b/LayoutTests/transitions/multiple-background-size-transitions.html
@@ -42,8 +42,8 @@
 
     const expectedValues = [
       // [time, element-id, property, expected-value, tolerance]
-      [0.5, 'box', '-webkit-background-size', [25, 25], 4],
-      [0.5, 'box1', '-webkit-mask-size', [25, 25], 4],
+      [0.5, 'box', '-webkit-background-size', "25% 25%, 25% 25%", 4],
+      [0.5, 'box1', '-webkit-mask-size', "25% 25%, 25% 25%", 4],
     ];
   
     function setupTest()