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 61 matching lines @@
 
    private:
     Member<CSSPaintValue> m_ownerValue;
   };
 
   void paintImageGeneratorReady();
 
   Member<CSSCustomIdentValue> m_name;
   Member<CSSPaintImageGenerator> m_generator;
   Member<Observer> m_paintImageGeneratorObserver;
+  Member<CSSStyleValueVector> m_parsedInputArguments;

[meade_UTC10, 2017/02/17 07:09:37]

Sorry if I mislead you when we had our chat earlier.. but isn't
CSSStyleValueVector already a HeapVector<Member<CSSStyleValue>>? You shouldn't
need a pointer to a vector...

[renjieliu1, 2017/02/19 04:39:14]

If I don't put it into member, the compiler tells me that class 'CSSPaintValue'
has untraced fields that require tracing.

   Vector<RefPtr<CSSVariableData>> m_argumentVariableData;
 };
 
 DEFINE_CSS_VALUE_TYPE_CASTS(CSSPaintValue, isPaintValue());
 
 }  // namespace blink
 
 #endif  // CSSPaintValue_h