Avoid false-positives of under-invalidation checking

Source/platform/graphics/paint/DrawingDisplayItem.h

 // Copyright 2014 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 DrawingDisplayItem_h
 #define DrawingDisplayItem_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatPoint.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "third_party/skia/include/core/SkPicture.h"
 #include "wtf/PassOwnPtr.h"
 
 namespace blink {
 
 class PLATFORM_EXPORT DrawingDisplayItem : public DisplayItem {
 public:
+#if ENABLE(ASSERT)
+    enum UnderInvalidationCheckingMode {
+        CheckPicture, // Check if the new picture and the old picture are the same
+        CheckBitmap, // Check if the new picture and the old picture produce the same bitmap
+        DontCheck // Skip for known bugs. Each usage should have a FIXME and a link to the bug.
+    };
+#endif
+
+    DrawingDisplayItem(const DisplayItemClientWrapper& client, Type type, PassRefPtr<const SkPicture> picture)
+        : DisplayItem(client, type)
+        , m_picture(picture && picture->approximateOpCount() ? picture : nullptr)
+#if ENABLE(ASSERT)
+        , m_underInvalidationCheckingMode(CheckPicture)
+#endif
+    {
+        ASSERT(isDrawingType(type));
+    }
+
     static PassOwnPtr<DrawingDisplayItem> create(const DisplayItemClientWrapper& client, Type type, PassRefPtr<const SkPicture> picture)
     {
         return adoptPtr(new DrawingDisplayItem(client, type, picture));
     }
 
     virtual void replay(GraphicsContext&);
     virtual void appendToWebDisplayItemList(WebDisplayItemList*) const override;
     virtual bool drawsContent() const override;
 
     PassRefPtr<const SkPicture> picture() const { return m_picture; }
 
-    DrawingDisplayItem(const DisplayItemClientWrapper& client, Type type, PassRefPtr<const SkPicture> picture)
-        : DisplayItem(client, type)
-        , m_picture(picture && picture->approximateOpCount() ? picture : nullptr)
 #if ENABLE(ASSERT)
-        , m_skipUnderInvalidationChecking(false)
-#endif
-    {
-        ASSERT(isDrawingType(type));
-    }
-
-#if ENABLE(ASSERT)
-    void setSkipUnderInvalidationChecking() { m_skipUnderInvalidationChecking = true; }
-    bool skipUnderInvalidationChecking() const { return m_skipUnderInvalidationChecking; }
+    void setUnderInvalidationCheckingMode(UnderInvalidationCheckingMode mode) { m_underInvalidationCheckingMode = mode; }
+    UnderInvalidationCheckingMode underInvalidationCheckingMode() const { return m_underInvalidationCheckingMode; }
 #endif
 
 private:
 #ifndef NDEBUG
     virtual void dumpPropertiesAsDebugString(WTF::StringBuilder&) const override;
 #endif
 
     RefPtr<const SkPicture> m_picture;
 
 #if ENABLE(ASSERT)
-    bool m_skipUnderInvalidationChecking;
+    UnderInvalidationCheckingMode m_underInvalidationCheckingMode;
 #endif
 };
 
 } // namespace blink
 
 #endif // DrawingDisplayItem_h