Blink-side contiguous allocation of 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 ed8985384fd6aee80bffa12ab56447a5271950e0..dabad7fbe01dd8383d5bde7434db4737e0b83471 100644
--- a/Source/platform/graphics/paint/DisplayItem.h
+++ b/Source/platform/graphics/paint/DisplayItem.h
@@ -24,7 +24,7 @@ class WebDisplayItemList;
 class PLATFORM_EXPORT DisplayItem {
 public:
     enum {
-        // Must be kept in sync with core/layout/PaintPhase.h.
+        // Must be kept in sync with core/paint/PaintPhase.h.
         PaintPhaseMax = 12,
     };
 
@@ -173,9 +173,34 @@ public:
         EndSubtreePaintPhaseLast = EndSubtreePaintPhaseFirst + PaintPhaseMax,
         EndSubtreeLast = EndSubtreePaintPhaseLast,
 
-        TypeLast = EndSubtreeLast
+        UninitializedType,

[jbroman, 2015/06/29 18:11:56]

Superduper nit: to me it seems nicer for the in-memory representation of this to
be zero. WDYT?

[pdr., 2015/06/29 22:20:03]

Oops, I landed this in the BoxClipper patch
(https://codereview.chromium.org/1212293003) without addressing this.

Lets fix this in a followup to keep this patch reviewable, but I agree 100%.

+        TypeLast = UninitializedType
     };
 
+    DisplayItem()

[chrishtr, 2015/06/29 17:19:16]

Add a comment about the use case. Also maybe private and friend classe'ed.

[pdr., 2015/06/29 22:20:03]

Moved to private and just friended ListContainer::appendByMoving. Also added a
comment explaining wtf.

+        : m_client(nullptr)
+        , m_scopeContainer(nullptr)
+        , m_scopeId(0)
+        , m_type(UninitializedType)
+        , m_skippedCache(false)
+        , m_ignoredFromList(true)
+#ifndef NDEBUG
+        , m_clientDebugString("invalid")
+#endif
+    { }
+
+    DisplayItem(const DisplayItemClientWrapper& client, Type type)
+        : m_client(client.displayItemClient())
+        , m_scopeContainer(nullptr)
+        , m_scopeId(0)
+        , m_type(type)
+        , m_skippedCache(false)
+        , m_ignoredFromList(false)
+#ifndef NDEBUG
+        , m_clientDebugString(client.debugName())
+#endif
+    { }
+
     struct Id {
         Id(DisplayItemClient c, Type t) : client(c), type(t), scopeId(0), scopeContainer(nullptr)
         {
@@ -303,6 +328,9 @@ public:
 
     virtual bool drawsContent() const { return false; }
 
+    bool ignoreFromDisplayList() const { return m_ignoredFromList; }
+    void setIgnoredFromDisplayList() { m_ignoredFromList = true; }
+
 #ifndef NDEBUG
     static WTF::String typeAsDebugString(DisplayItem::Type);
     const WTF::String& clientDebugString() const { return m_clientDebugString; }
@@ -310,18 +338,6 @@ public:
     virtual void dumpPropertiesAsDebugString(WTF::StringBuilder&) const;
 #endif
 
-protected:
-    DisplayItem(const DisplayItemClientWrapper& client, Type type)
-        : m_client(client.displayItemClient())
-        , m_scopeContainer(nullptr)
-        , m_scopeId(0)
-        , m_type(type)
-        , m_skippedCache(false)
-#ifndef NDEBUG
-        , m_clientDebugString(client.debugName())
-#endif
-    { }
-
 private:
     const DisplayItemClient m_client;
     DisplayItemClient m_scopeContainer;
@@ -329,6 +345,7 @@ private:
     static_assert(TypeLast < (1 << 16), "DisplayItem::Type should fit in 16 bits");
     const Type m_type : 16;
     unsigned m_skippedCache : 1;
+    unsigned m_ignoredFromList : 1;
 
 #ifndef NDEBUG
     WTF::String m_clientDebugString;