Allow transitions on background-size with positionally matched keywords

third_party/WebKit/LayoutTests/animations/interpolation/border-image-width-interpolation.html

Index: third_party/WebKit/LayoutTests/animations/interpolation/border-image-width-interpolation.html
diff --git a/third_party/WebKit/LayoutTests/animations/interpolation/border-image-width-interpolation.html b/third_party/WebKit/LayoutTests/animations/interpolation/border-image-width-interpolation.html
index 1dc7d25891ca9666ef69b1af3a7ed73fc4ad3dd3..956857881615d407544a7a33aa1176d42c2a513d 100644
--- a/third_party/WebKit/LayoutTests/animations/interpolation/border-image-width-interpolation.html
+++ b/third_party/WebKit/LayoutTests/animations/interpolation/border-image-width-interpolation.html
@@ -142,11 +142,19 @@ assertInterpolation({
   {at: 1.5,  is: 'calc(-5px + 30%)'}, // Should be parsed as -5px + 36px = 31px
 ]);
 
-assertNoInterpolation({
+assertInterpolation({
   property: 'border-image-width',
   from: '10px auto auto 20',
   to: '110px auto auto 120'
-});
+}, [
+  {at: -0.3, is: '  0px auto auto   0'},
+  {at: 0,    is: ' 10px auto auto  20'},
+  {at: 0.3,  is: ' 40px auto auto  50'},
+  {at: 0.6,  is: ' 70px auto auto  80'},
+  {at: 1,    is: '110px auto auto 120'},
+  {at: 1.5,  is: '160px auto auto 170'},
+]);
+
 assertNoInterpolation({
   property: 'border-image-width',
   from: '10px auto auto 20',