Implement CSSPaintValue and add a layout test.

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CSSPaintValue_h
 #define CSSPaintValue_h
 
 #include "core/css/CSSCustomIdentValue.h"
 #include "core/css/CSSImageGeneratorValue.h"
 #include "core/css/CSSPaintImageGenerator.h"
@@ skipping 58 matching lines @@
     }
 
     void paintImageGeneratorReady() final;
 
    private:
     Member<CSSPaintValue> m_ownerValue;
   };
 
   void paintImageGeneratorReady();
 
+  bool parseInputArguments();
+
+  bool m_inputArgumentsInvalid = false;
+
   Member<CSSCustomIdentValue> m_name;
   Member<CSSPaintImageGenerator> m_generator;
   Member<Observer> m_paintImageGeneratorObserver;
+  Member<CSSStyleValueVector> m_parsedInputArguments;
   Vector<RefPtr<CSSVariableData>> m_argumentVariableData;
 };
 
 DEFINE_CSS_VALUE_TYPE_CASTS(CSSPaintValue, isPaintValue());
 
 }  // namespace blink
 
 #endif  // CSSPaintValue_h