Add additive animation support for CSS properties perspective-origin and object-position

third_party/WebKit/Source/core/animation/CSSPositionAxisListInterpolationType.cpp

Index: third_party/WebKit/Source/core/animation/CSSPositionAxisListInterpolationType.cpp
diff --git a/third_party/WebKit/Source/core/animation/CSSPositionAxisListInterpolationType.cpp b/third_party/WebKit/Source/core/animation/CSSPositionAxisListInterpolationType.cpp
index 93d79823aaaa3af4b6158a7f75e8120fd7e84fad..2aeb6d294c31527ba17de6d0d1428d1afec6a6a2 100644
--- a/third_party/WebKit/Source/core/animation/CSSPositionAxisListInterpolationType.cpp
+++ b/third_party/WebKit/Source/core/animation/CSSPositionAxisListInterpolationType.cpp
@@ -12,17 +12,34 @@
 
 namespace blink {
 
-static InterpolationValue convertPositionAxisCSSValue(const CSSValue& value)
+InterpolationValue CSSPositionAxisListInterpolationType::convertPositionAxisCSSValue(const CSSValue& value)
 {
-    if (!value.isValuePair())
+    if (value.isValuePair()) {
+        const CSSValuePair& pair = toCSSValuePair(value);
+        InterpolationValue result = CSSLengthInterpolationType::maybeConvertCSSValue(pair.second());
+        CSSValueID side = toCSSPrimitiveValue(pair.first()).getValueID();
+        if (side == CSSValueRight || side == CSSValueBottom)
+            CSSLengthInterpolationType::subtractFromOneHundredPercent(result);
+        return result;
+    }
+
+    const CSSPrimitiveValue& primitveValue = toCSSPrimitiveValue(value);
+    if (!primitveValue.isValueID())
         return CSSLengthInterpolationType::maybeConvertCSSValue(value);
 
-    const CSSValuePair& pair = toCSSValuePair(value);
-    InterpolationValue result = CSSLengthInterpolationType::maybeConvertCSSValue(pair.second());
-    CSSValueID side = toCSSPrimitiveValue(pair.first()).getValueID();
-    if (side == CSSValueRight || side == CSSValueBottom)
-        CSSLengthInterpolationType::subtractFromOneHundredPercent(result);
-    return result;
+    switch (primitveValue.getValueID()) {
+    case CSSValueLeft:
+    case CSSValueTop:
+        return CSSLengthInterpolationType::createInterpolablePercent(0);
+    case CSSValueRight:
+    case CSSValueBottom:
+        return CSSLengthInterpolationType::createInterpolablePercent(100);
+    case CSSValueCenter:
+        return CSSLengthInterpolationType::createInterpolablePercent(50);
+    default:
+        ASSERT_NOT_REACHED();
+        return nullptr;
+    }
 }
 
 InterpolationValue CSSPositionAxisListInterpolationType::maybeConvertValue(const CSSValue& value, const StyleResolverState&, ConversionCheckers&) const