Add smooth interpolation support for <color> custom properties

third_party/WebKit/Source/core/css/CSSSyntaxDescriptor.h

Index: third_party/WebKit/Source/core/css/CSSSyntaxDescriptor.h
diff --git a/third_party/WebKit/Source/core/css/CSSSyntaxDescriptor.h b/third_party/WebKit/Source/core/css/CSSSyntaxDescriptor.h
index 94eb4326a2f0a8cc1c21c06e5ed54137b54728bd..ff4daceff1065219ab459ab89f23c5386c142cd4 100644
--- a/third_party/WebKit/Source/core/css/CSSSyntaxDescriptor.h
+++ b/third_party/WebKit/Source/core/css/CSSSyntaxDescriptor.h
@@ -5,6 +5,7 @@
 #ifndef CSSSyntaxDescriptor_h
 #define CSSSyntaxDescriptor_h
 
+#include "core/animation/InterpolationTypesMap.h"
 #include "core/css/parser/CSSParserTokenRange.h"
 
 namespace blink {
@@ -52,6 +53,9 @@ class CORE_EXPORT CSSSyntaxDescriptor {
            m_syntaxComponents[0].m_type == CSSSyntaxType::TokenStream;
   }
 
+  InterpolationTypes createInterpolationTypes(
+      const AtomicString& propertyName) const;
+
  private:
   Vector<CSSSyntaxComponent> m_syntaxComponents;
 };