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..c7bff39d2bcb5fd9dc6210c0202e7864d7c09053 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 +23,10 @@ public:
 private:
     InterpolationValue maybeConvertValue(const CSSValue& value, const StyleResolverState&, ConversionCheckers&) const final
     {
+        if (value.isPrimitiveValue()) {
+            DCHECK(toCSSPrimitiveValue(value).getValueID() == CSSValueAuto);
+            return nullptr;
+        }

[alancutter (OOO until 2018), 2016/09/22 08:05:47]

This can just be !value.isPairValue(). InterpolationTypes ideally don't need to
be aware of specific property details.

[Eric Willigers, 2016/09/22 09:57:06]

Done.

         const CSSValuePair& pair = toCSSValuePair(value);
         return ListInterpolationFunctions::createList(2, [&pair](size_t index) {
             return CSSPositionAxisListInterpolationType::convertPositionAxisCSSValue(index == 0 ? pair.first() : pair.second());