Avoid re-iterate out-of-order display items

Source/platform/graphics/paint/DisplayItem.h

Index: Source/platform/graphics/paint/DisplayItem.h
diff --git a/Source/platform/graphics/paint/DisplayItem.h b/Source/platform/graphics/paint/DisplayItem.h
index 55f0db17720c57a732e940235ab47d5a6b2e1887..d9a811653199a5608e12ae52b44ed8040a500f32 100644
--- a/Source/platform/graphics/paint/DisplayItem.h
+++ b/Source/platform/graphics/paint/DisplayItem.h
@@ -184,7 +184,6 @@ public:
         , m_type(type)
         , m_derivedSize(derivedSize)
         , m_skippedCache(false)
-        , m_ignoredFromList(false)
 #ifndef NDEBUG
         , m_clientDebugString(client.debugName())
 #endif
@@ -329,8 +328,8 @@ public:
 
     virtual bool drawsContent() const { return false; }
 
-    bool ignoreFromDisplayList() const { return m_ignoredFromList; }
-    void setIgnoredFromDisplayList() { m_ignoredFromList = true; }
+    bool isValid() const { return m_client; }
+    void invalidate() { new (this) DisplayItem; }

[pdr., 2015/08/17 23:28:50]

Will this run the DisplayItem subclass destructors?

The in-place new constructor is rarely used in blink. Can you add a comment such
as:
// Re-construct this display item as a permanently invalid item with no client
set.

[Xianzhu, 2015/08/17 23:46:58]

No but needed. Added an in-place destructor call.
Done.

 
 #ifndef NDEBUG
     static WTF::String typeAsDebugString(DisplayItem::Type);
@@ -351,7 +350,6 @@ private:
         , m_type(UninitializedType)
         , m_derivedSize(sizeof(*this))
         , m_skippedCache(false)
-        , m_ignoredFromList(true)
 #ifndef NDEBUG
         , m_clientDebugString("invalid")
 #endif
@@ -363,7 +361,6 @@ private:
     const Type m_type : 16;
     unsigned m_derivedSize : 8; // size of the actual derived class
     unsigned m_skippedCache : 1;
-    unsigned m_ignoredFromList : 1;
 
 #ifndef NDEBUG
     WTF::String m_clientDebugString;