Add additive animation support for CSS property background-position

third_party/WebKit/LayoutTests/animations/interpolation/background-position-origin-interpolation.html

Index: third_party/WebKit/LayoutTests/animations/interpolation/background-position-origin-interpolation.html
diff --git a/third_party/WebKit/LayoutTests/animations/interpolation/background-position-origin-interpolation.html b/third_party/WebKit/LayoutTests/animations/interpolation/background-position-origin-interpolation.html
index de91281b65264ea11026e7f0be5f017a5861a95c..14ccc9234df699fbe7b179631d57643a7868bc44 100644
--- a/third_party/WebKit/LayoutTests/animations/interpolation/background-position-origin-interpolation.html
+++ b/third_party/WebKit/LayoutTests/animations/interpolation/background-position-origin-interpolation.html
@@ -96,11 +96,11 @@ assertInterpolation({
   from: 'center center',
   to: 'center top 20px',
 }, [
-  {at: 0, is: 'left 50% top 50%'},
-  {at: 0.25, is: 'left 50% top calc(5px + 37.5%)'},
-  {at: 0.5, is: 'left 50% top calc(10px + 25%)'},
-  {at: 0.75, is: 'left 50% top calc(15px + 12.5%)'},
-  {at: 1, is: 'left 50% top 20px'},
+  {at: 0, is: '50% 50%'},
+  {at: 0.25, is: '50% calc(5px + 37.5%)'},
+  {at: 0.5, is: '50% calc(10px + 25%)'},
+  {at: 0.75, is: '50% calc(15px + 12.5%)'},
+  {at: 1, is: '50% 20px'},
 ]);
 
 // right-top
@@ -122,11 +122,11 @@ assertInterpolation({
   from: 'center center',
   to: 'left 20px center',
 }, [
-  {at: 0, is: 'left 50% top 50%'},
-  {at: 0.25, is: 'left calc(5px + 37.5%) top 50%'},
-  {at: 0.5, is: 'left calc(10px + 25%) top 50%'},
-  {at: 0.75, is: 'left calc(15px + 12.5%) top 50%'},
-  {at: 1, is: 'left 20px top 50%'},
+  {at: 0, is: '50% 50%'},
+  {at: 0.25, is: 'calc(5px + 37.5%) 50%'},
+  {at: 0.5, is: 'calc(10px + 25%) 50%'},
+  {at: 0.75, is: 'calc(15px + 12.5%) 50%'},
+  {at: 1, is: '20px 50%'},
 ]);
 
 // center-center
@@ -148,11 +148,11 @@ assertInterpolation({
   from: 'center center',
   to: 'right 20px center',
 }, [
-  {at: 0, is: 'left 50% top 50%'},
-  {at: 0.25, is: 'left calc(-5px + 62.5%) top 50%'},
-  {at: 0.5, is: 'left calc(-10px + 75%) top 50%'},
-  {at: 0.75, is: 'left calc(-15px + 87.5%) top 50%'},
-  {at: 1, is: 'left calc(-20px + 100%) top 50%'},
+  {at: 0, is: '50% 50%'},
+  {at: 0.25, is: 'calc(-5px + 62.5%) 50%'},
+  {at: 0.5, is: 'calc(-10px + 75%) 50%'},
+  {at: 0.75, is: 'calc(-15px + 87.5%) 50%'},
+  {at: 1, is: 'calc(-20px + 100%) 50%'},
 ]);
 
 // left-bottom
@@ -174,11 +174,11 @@ assertInterpolation({
   from: 'center center',
   to: 'center bottom 20px',
 }, [
-  {at: 0, is: 'left 50% top 50%'},
-  {at: 0.25, is: 'left 50% top calc(-5px + 62.5%)'},
-  {at: 0.5, is: 'left 50% top calc(-10px + 75%)'},
-  {at: 0.75, is: 'left 50% top calc(-15px + 87.5%)'},
-  {at: 1, is: 'left 50% top calc(-20px + 100%)'},
+  {at: 0, is: '50% 50%'},
+  {at: 0.25, is: '50% calc(-5px + 62.5%)'},
+  {at: 0.5, is: '50% calc(-10px + 75%)'},
+  {at: 0.75, is: '50% calc(-15px + 87.5%)'},
+  {at: 1, is: '50% calc(-20px + 100%)'},
 ]);
 
 // right-bottom
@@ -193,5 +193,18 @@ assertInterpolation({
   {at: 0.75, is: 'calc(-15px + 87.5%) calc(-15px + 87.5%)'},
   {at: 1, is: 'calc(-20px + 100%) calc(-20px + 100%)'},
 ]);
+
+// Single values
+assertInterpolation({
+  property: 'background-position',
+  from: 'center',
+  to: 'bottom',
+}, [
+  {at: 0, is: '50% 50%'},
+  {at: 0.25, is: '50% 62.5%'},
+  {at: 0.5, is: '50% 75%'},
+  {at: 0.75, is: '50% 87.5%'},
+  {at: 1, is: '50% 100%'},
+]);
 </script>
 </body>