New display item caching

Source/platform/graphics/paint/CachedDisplayItem.h

Index: Source/platform/graphics/paint/CachedDisplayItem.h
diff --git a/Source/platform/graphics/paint/CachedDisplayItem.h b/Source/platform/graphics/paint/CachedDisplayItem.h
index c5d55359352059aa32400ec138328f8202bf3ab9..706235dc2fee9dedaaf657cc2bc0e13250bd2605 100644
--- a/Source/platform/graphics/paint/CachedDisplayItem.h
+++ b/Source/platform/graphics/paint/CachedDisplayItem.h
@@ -5,6 +5,7 @@
 #ifndef CachedDisplayItem_h
 #define CachedDisplayItem_h
 
+#include "platform/geometry/FloatRect.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "wtf/Assertions.h"
 
@@ -21,17 +22,34 @@ public:
         return adoptPtr(new CachedDisplayItem(client, type));
     }
 
+#ifndef NDEBUG
+    static PassOwnPtr<CachedDisplayItem> create(DisplayItemClient client, Type type, const FloatRect& bounds)
+    {
+        return adoptPtr(new CachedDisplayItem(client, type, bounds));
+    }
+#endif
+
     virtual bool isCached() const { return true; }
 
 private:
     CachedDisplayItem(DisplayItemClient client, Type type) : DisplayItem(client, type) { }
 
+#ifdef NDEBUG
     // CachedDisplayItem is never replayed or appended to WebDisplayItemList.
-    virtual void replay(GraphicsContext*) override final { ASSERT_NOT_REACHED(); }
-    virtual void appendToWebDisplayItemList(WebDisplayItemList*) const override final { ASSERT_NOT_REACHED(); }
+    virtual void replay(GraphicsContext*) final { ASSERT_NOT_REACHED(); }
+    virtual void appendToWebDisplayItemList(WebDisplayItemList*) const final { ASSERT_NOT_REACHED(); }
+#else
+    CachedDisplayItem(DisplayItemClient client, Type type, const FloatRect& bounds)
+        : DisplayItem(client, type)
+        , m_bounds(bounds) { }
+
+    // Generates red rectangle to indicate under-invalidation errors.
+    virtual void replay(GraphicsContext*) final;
+    virtual void appendToWebDisplayItemList(WebDisplayItemList*) const final;
 
-#ifndef NDEBUG
     virtual const char* name() const override { return "Cached"; }
+
+    const FloatRect m_bounds;
 #endif
 };