Hook up style invalidation for CSS Paint API.

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 17 matching lines @@
     bool isFixedSize() const { return false; }
     IntSize fixedSize(const LayoutObject&) { return IntSize(); }
 
     bool isPending() const { return false; }
     bool knownToBeOpaque(const LayoutObject&) const { return false; }
 
     void loadSubimages(Document*) { }
 
     bool equals(const CSSPaintValue&) const;
 
+    const Vector<CSSPropertyID>& nativeInvalidationProperties() const
+    {
+        DCHECK(m_generator);

[ikilpatrick, 2016/04/19 22:31:25]

This is potentially bad, the m_generator doesn't exist until paint() is called
(as it needs the Document to look up the paint worklet).

In ComputedStyle this could be protected against by a needsFirstPaint() check,
i.e.

// CSSPaintValue.h
bool needsFirstPaint() { return !m_generator; }

// ComputedStyle.h
bool ComputedStyle::diffNeedsPaintInvalidationObjectForPaint(styleImage)
{
  if (paintValue->needsFirstPaint())
    return true;
}

I.e. a paint function which has never been painted is always invalid.

+        return m_generator->nativeInvalidationProperties();
+    }
+    const Vector<AtomicString>& customInvalidationProperties() const
+    {
+        DCHECK(m_generator);
+        return m_generator->customInvalidationProperties();
+    }
+
     DECLARE_TRACE_AFTER_DISPATCH();
 
 private:
     explicit CSSPaintValue(CSSCustomIdentValue* name);
 
     class Observer final : public CSSPaintImageGenerator::Observer {
         WTF_MAKE_NONCOPYABLE(Observer);
     public:
         explicit Observer(CSSPaintValue* ownerValue)
             : m_ownerValue(ownerValue)
@@ skipping 17 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