Add additive animation support for CSS property clip

third_party/WebKit/LayoutTests/animations/interpolation/clip-interpolation.html

Index: third_party/WebKit/LayoutTests/animations/interpolation/clip-interpolation.html
diff --git a/third_party/WebKit/LayoutTests/animations/interpolation/clip-interpolation.html b/third_party/WebKit/LayoutTests/animations/interpolation/clip-interpolation.html
index a49f6e01144442632642c8e718176cb4b2f043b4..48709b7d0b6f6fd47086d6c053086355c9f6f006 100644
--- a/third_party/WebKit/LayoutTests/animations/interpolation/clip-interpolation.html
+++ b/third_party/WebKit/LayoutTests/animations/interpolation/clip-interpolation.html
@@ -79,31 +79,17 @@ assertInterpolation({
   {at: 2, is: 'rect(0px, 125px, 100px, 0px)'},
 ]);
 
-assertInterpolation({
+assertNoInterpolation({
   property: 'clip',
   from: 'rect(auto, auto, auto, 10px)',
   to: 'rect(20px, 50px, 50px, auto)'
-}, [
-  {at: -1, is: 'rect(auto, auto, auto, 10px)'},
-  {at: 0, is: 'rect(auto, auto, auto, 10px)'},
-  {at: 0.25, is: 'rect(auto, auto, auto, 10px)'},
-  {at: 0.75, is: 'rect(20px, 50px, 50px, auto)'},
-  {at: 1, is: 'rect(20px, 50px, 50px, auto)'},
-  {at: 2, is: 'rect(20px, 50px, 50px, auto)'}
-]);
+});
 
-assertInterpolation({
+assertNoInterpolation({
   property: 'clip',
   from: 'rect(auto, 0px, auto, 10px)',
   to: 'rect(auto, 50px, 50px, auto)'
-}, [
-  {at: -1, is: 'rect(auto, -50px, auto, 10px)'},
-  {at: 0, is: 'rect(auto, 0px, auto, 10px)'},
-  {at: 0.25, is: 'rect(auto, 12.5px, auto, 10px)'},
-  {at: 0.75, is: 'rect(auto, 37.5px, 50px, auto)'},
-  {at: 1, is: 'rect(auto, 50px, 50px, auto)'},
-  {at: 2, is: 'rect(auto, 100px, 50px, auto)'}
-]);
+});
 
 assertNoInterpolation({
   property: 'clip',