Separate display item clients for negative and normal/positive z-order children

third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h

Index: third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h b/third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h
index 35e1c414162c22fa4b24b1096f2952386b21678f..8bfb58e1646eec4b4a82927be7e90ad77eea50ff 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h
@@ -168,14 +168,9 @@ public:
         BeginFixedPositionContainer,
         EndFixedPositionContainer,
 
-        SubsequenceFirst,
-        SubsequenceNegativeZOrder = SubsequenceFirst,
-        SubsequenceNormalFlowAndPositiveZOrder,
-        SubsequenceLast = SubsequenceNormalFlowAndPositiveZOrder,
-        EndSubsequenceFirst,
-        EndSubsequenceLast = EndSubsequenceFirst + SubsequenceLast - SubsequenceFirst,
-        CachedSubsequenceFirst,
-        CachedSubsequenceLast = CachedSubsequenceFirst + SubsequenceLast - SubsequenceFirst,
+        Subsequence,
+        EndSubsequence,
+        CachedSubsequence,
 
         CachedDisplayItemList,
 
@@ -194,8 +189,9 @@ public:
     };
 
     DisplayItem(const DisplayItemClientWrapper& client, Type type, size_t derivedSize)
-        : m_client(client.displayItemClient())
+        : m_clientObject(client.displayItemClient().object)
         , m_scope(0)
+        , m_subClientId(client.displayItemClient().subClientId)
         , m_type(type)
         , m_derivedSize(derivedSize)
         , m_skippedCache(false)
@@ -223,7 +219,7 @@ public:
             // We should always convert to non-cached types before matching.
             ASSERT(!isCachedType(item.m_type));
             ASSERT(!isCachedType(type));
-            return client == item.m_client
+            return client == item.client()
                 && type == item.m_type
                 && scope == item.m_scope;
         }
@@ -238,20 +234,20 @@ public:
     {
         if (isCachedDrawingType(type))
             return cachedDrawingTypeToDrawingType(type);
-        if (isCachedSubsequenceType(type))
-            return cachedSubsequenceTypeToSubsequenceType(type);
+        if (type == CachedSubsequence)
+            return Subsequence;
         return type;
     }
 
     // Return the Id with cached type converted to non-cached type.
     Id nonCachedId() const
     {
-        return Id(m_client, nonCachedType(m_type), m_scope);
+        return Id(client(), nonCachedType(m_type), m_scope);
     }
 
     virtual void replay(GraphicsContext&) const { }
 
-    DisplayItemClient client() const { return m_client; }
+    DisplayItemClient client() const { return DisplayItemClient(m_clientObject, m_subClientId); }
     Type type() const { return m_type; }
 
     void setScope(unsigned scope) { m_scope = scope; }
@@ -319,13 +315,9 @@ public:
 
     DEFINE_PAIRED_CATEGORY_METHODS(Transform3D, transform3D)
 
-    DEFINE_PAIRED_CATEGORY_METHODS(Subsequence, subsequence)
-    DEFINE_CATEGORY_METHODS(CachedSubsequence)
-    DEFINE_CONVERSION_METHODS(Subsequence, subsequence, CachedSubsequence, cachedSubsequence)
-
-    static bool isCachedType(Type type) { return isCachedDrawingType(type) || isCachedSubsequenceType(type) || type == CachedDisplayItemList; }
+    static bool isCachedType(Type type) { return isCachedDrawingType(type) || type == CachedSubsequence || type == CachedDisplayItemList; }
     bool isCached() const { return isCachedType(m_type); }
-    static bool isCacheableType(Type type) { return isDrawingType(type) || isSubsequenceType(type); }
+    static bool isCacheableType(Type type) { return isDrawingType(type) || type == Subsequence; }
     bool isCacheable() const { return !skippedCache() && isCacheableType(m_type); }
 
     virtual bool isBegin() const { return false; }
@@ -335,7 +327,7 @@ public:
     virtual bool isEndAndPairedWith(DisplayItem::Type otherType) const { return false; }
     virtual bool equals(const DisplayItem& other) const
     {
-        return m_client == other.m_client
+        return client() == other.client()
             && m_scope == other.m_scope
             && m_type == other.m_type
             && m_derivedSize == other.m_derivedSize
@@ -345,7 +337,7 @@ public:
 
     virtual bool drawsContent() const { return false; }
 
-    bool isValid() const { return m_client; }
+    bool isValid() const { return m_clientObject; }
 
 #ifndef NDEBUG
     static WTF::String typeAsDebugString(DisplayItem::Type);
@@ -362,17 +354,23 @@ private:
     template <typename T, unsigned alignment> friend class ContiguousContainer;
 
     DisplayItem()
-        : m_client(nullptr)
+        : m_clientObject(nullptr)
         , m_scope(0)
+        , m_subClientId(0)
         , m_type(UninitializedType)
         , m_derivedSize(sizeof(*this))
         , m_skippedCache(false)
     { }
 
-    const DisplayItemClient m_client;
+    const DisplayItemClientObject m_clientObject;
     unsigned m_scope;
+
+    static_assert(kMaxSubDisplayItemClientId == (1 << 6) - 1, "subClientId should fit in 6 bits");
+    const unsigned m_subClientId : 6;
+
     static_assert(TypeLast < (1 << 16), "DisplayItem::Type should fit in 16 bits");
     const Type m_type : 16;
+
     const unsigned m_derivedSize : 8; // size of the actual derived class
     unsigned m_skippedCache : 1;