Implement CSSPaintValue and add a layout test.

third_party/WebKit/Source/core/css/CSSPaintImageGenerator.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 CSSPaintImageGenerator_h
 #define CSSPaintImageGenerator_h
 
 #include "core/CSSPropertyNames.h"
 #include "core/CoreExport.h"
 #include "platform/geometry/IntSize.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
+class CSSVariableData;
 class Document;
 class Image;
 class LayoutObject;
 
 // Produces a PaintGeneratedImage from a CSS Paint API callback.
 // https://drafts.css-houdini.org/css-paint-api/
 class CORE_EXPORT CSSPaintImageGenerator
     : public GarbageCollectedFinalized<CSSPaintImageGenerator> {
  public:
   // This observer is used if the paint worklet doesn't have a javascript
@@ skipping 15 matching lines @@
   typedef CSSPaintImageGenerator* (*CSSPaintImageGeneratorCreateFunction)(
       const String&,
       Document&,
       Observer*);
   static void init(CSSPaintImageGeneratorCreateFunction);
 
   // Invokes the CSS Paint API 'paint' callback. May return a nullptr
   // representing an invalid image if an error occurred.
   virtual PassRefPtr<Image> paint(const LayoutObject&,
                                   const IntSize&,
-                                  float zoom) = 0;
+                                  float zoom,
+                                  const Vector<RefPtr<CSSVariableData>>&) = 0;
 
   virtual const Vector<CSSPropertyID>& nativeInvalidationProperties() const = 0;
   virtual const Vector<AtomicString>& customInvalidationProperties() const = 0;
   virtual bool hasAlpha() const = 0;
 
   DEFINE_INLINE_VIRTUAL_TRACE() {}
 };
 
 }  // namespace blink
 
 #endif  // CSSPaintImageGenerator_h