CSS Motion Path: animate offset-anchor and offset-position

third_party/WebKit/Source/core/animation/CSSPositionInterpolationType.h

Index: third_party/WebKit/Source/core/animation/CSSPositionInterpolationType.h
diff --git a/third_party/WebKit/Source/core/animation/CSSPositionInterpolationType.h b/third_party/WebKit/Source/core/animation/CSSPositionInterpolationType.h
index 523542e0b575ea3fae5693fa19166742c32261a0..8c7bfa1ee5a74811dd9f326baa4bd74838344302 100644
--- a/third_party/WebKit/Source/core/animation/CSSPositionInterpolationType.h
+++ b/third_party/WebKit/Source/core/animation/CSSPositionInterpolationType.h
@@ -9,6 +9,7 @@
 
 #include "core/animation/CSSPositionAxisListInterpolationType.h"
 #include "core/animation/ListInterpolationFunctions.h"
+#include "core/css/CSSPrimitiveValue.h"
 #include "core/css/CSSValuePair.h"
 
 namespace blink {
@@ -22,6 +23,9 @@ public:
 private:
     InterpolationValue maybeConvertValue(const CSSValue& value, const StyleResolverState&, ConversionCheckers&) const final
     {
+        if (!value.isValuePair()) {
+            return nullptr;
+        }
         const CSSValuePair& pair = toCSSValuePair(value);
         return ListInterpolationFunctions::createList(2, [&pair](size_t index) {
             return CSSPositionAxisListInterpolationType::convertPositionAxisCSSValue(index == 0 ? pair.first() : pair.second());