Extend PropertyHandle to include custom property identifiers

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

Index: third_party/WebKit/Source/core/animation/AnimationInputHelpers.cpp
diff --git a/third_party/WebKit/Source/core/animation/AnimationInputHelpers.cpp b/third_party/WebKit/Source/core/animation/AnimationInputHelpers.cpp
index efee1088b2d1538a71cbbfbbb2bc666c2589f82d..a422897c58ea9204ccc865b543ac33f15fc0545e 100644
--- a/third_party/WebKit/Source/core/animation/AnimationInputHelpers.cpp
+++ b/third_party/WebKit/Source/core/animation/AnimationInputHelpers.cpp
@@ -32,6 +32,8 @@ static String removeSVGPrefix(const String& property)
 
 CSSPropertyID AnimationInputHelpers::keyframeAttributeToCSSProperty(const String& property, const Document& document)
 {
+    // TODO(crbug.com/644148): Allow custom properties that begin with "--".
+
     // Disallow prefixed properties.
     if (property[0] == '-' || isASCIIUpper(property[0]))
         return CSSPropertyInvalid;