Add "alpha" option to PaintWorklet

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

 // 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.
 
 #include "core/css/CSSPaintValue.h"
 
 #include "core/css/CSSCustomIdentValue.h"
 #include "core/layout/LayoutObject.h"
 #include "platform/graphics/Image.h"
 #include "wtf/text/StringBuilder.h"
@@ skipping 38 matching lines @@
     m_ownerValue->paintImageGeneratorReady();
 }
 
 void CSSPaintValue::paintImageGeneratorReady()
 {
     for (const LayoutObject* client : clients().keys()) {
         const_cast<LayoutObject*>(client)->imageChanged(static_cast<WrappedImagePtr>(this));
     }
 }
 
+bool CSSPaintValue::knownToBeOpaque(const LayoutObject& layoutObject) const
+{
+    return m_generator && !m_generator->hasAlpha();
+}
+
 bool CSSPaintValue::equals(const CSSPaintValue& other) const
 {
     return name() == other.name();
 }
 
 DEFINE_TRACE_AFTER_DISPATCH(CSSPaintValue)
 {
     visitor->trace(m_name);
     visitor->trace(m_generator);
     visitor->trace(m_paintImageGeneratorObserver);
     CSSImageGeneratorValue::traceAfterDispatch(visitor);
 }
 
 } // namespace blink