Add "alpha" option to PaintWorklet

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 11 matching lines @@
 
     String customCSSText() const;
 
     String name() const;
 
     PassRefPtr<Image> image(const LayoutObject&, const IntSize&);
     bool isFixedSize() const { return false; }
     IntSize fixedSize(const LayoutObject&) { return IntSize(); }
 
     bool isPending() const { return true; }
-    bool knownToBeOpaque(const LayoutObject&) const { return false; }
+    bool knownToBeOpaque(const LayoutObject&) const;
 
     void loadSubimages(Document*) { }
 
     bool equals(const CSSPaintValue&) const;
 
     const Vector<CSSPropertyID>* nativeInvalidationProperties() const
     {
         return m_generator ? &m_generator->nativeInvalidationProperties() : nullptr;
     }
     const Vector<AtomicString>* customInvalidationProperties() const
@@ skipping 31 matching lines @@
     Member<CSSCustomIdentValue> m_name;
     Member<CSSPaintImageGenerator> m_generator;
     Member<Observer> m_paintImageGeneratorObserver;
 };
 
 DEFINE_CSS_VALUE_TYPE_CASTS(CSSPaintValue, isPaintValue());
 
 } // namespace blink
 
 #endif // CSSPaintValue_h