Make flex-grow and flex-shrink interpolation continuous with 0

LayoutTests/animations/interpolation/flex-grow-interpolation.html

Index: LayoutTests/animations/interpolation/flex-grow-interpolation.html
diff --git a/LayoutTests/animations/interpolation/flex-grow-interpolation.html b/LayoutTests/animations/interpolation/flex-grow-interpolation.html
index 90b13150d67c99ac18c1cf075287b7670185c6a4..d09cd3895da89e45967d188524440f977d6c231d 100644
--- a/LayoutTests/animations/interpolation/flex-grow-interpolation.html
+++ b/LayoutTests/animations/interpolation/flex-grow-interpolation.html
@@ -40,11 +40,18 @@ assertInterpolation({
   {at: 1.5, is: '2.5'},
 ]);
 
-assertNoInterpolation({
+assertInterpolation({
   property: 'flex-grow',
   from: 'initial',
   to: '2',
-});
+}, [
+  {at: -0.3, is: '0'},
+  {at: 0, is: '0'},
+  {at: 0.3, is: '0.6'},
+  {at: 0.6, is: '1.2'},
+  {at: 1, is: '2'},
+  {at: 1.5, is: '3'},
+]);
 
 assertInterpolation({
   property: 'flex-grow',
@@ -59,11 +66,18 @@ assertInterpolation({
   {at: 1.5, is: '1.5'},
 ]);
 
-assertNoInterpolation({
+assertInterpolation({
   property: 'flex-grow',
   from: 'unset',
   to: '2',
-});
+}, [
+  {at: -0.3, is: '0'},
+  {at: 0, is: '0'},
+  {at: 0.3, is: '0.6'},
+  {at: 0.6, is: '1.2'},
+  {at: 1, is: '2'},
+  {at: 1.5, is: '3'},
+]);
 
 assertInterpolation({
   property: 'flex-grow',
@@ -76,13 +90,21 @@ assertInterpolation({
   {at: 0.3, is: '1.3'},
   {at: 0.6, is: '1.6'},
   {at: 1, is: '2'},
-  {at: 1.5, is: '2.5'}
+  {at: 1.5, is: '2.5'},
 ]);
 
-assertNoInterpolation({
+assertInterpolation({
   property: 'flex-grow',
   from: '0',
   to: '1',
-});
+}, [
+  {at: -5, is: '0'},
+  {at: -0.3, is: '0'},
+  {at: 0, is: '0'},
+  {at: 0.3, is: '0.3'},
+  {at: 0.6, is: '0.6'},
+  {at: 1, is: '1'},
+  {at: 1.5, is: '1.5'},
+]);
 </script>
 </body>