Slimming Paint phase 2 compositing algorithm plumbing

Source/platform/graphics/paint/DisplayItemList.cpp

Index: Source/platform/graphics/paint/DisplayItemList.cpp
diff --git a/Source/platform/graphics/paint/DisplayItemList.cpp b/Source/platform/graphics/paint/DisplayItemList.cpp
index 928ddcaf1ea4e707768cc06e0cb71ef748917053..8a66d0c723c1491684403b72ab143d992878312c 100644
--- a/Source/platform/graphics/paint/DisplayItemList.cpp
+++ b/Source/platform/graphics/paint/DisplayItemList.cpp
@@ -223,7 +223,9 @@ void DisplayItemList::copyCachedSubtree(DisplayItems::iterator& currentIt, Displ
 // The algorithm is O(|m_currentDisplayItems| + |m_newDisplayItems|).
 // Coefficients are related to the ratio of out-of-order [Subtree]CachedDisplayItems
 // and the average number of (Drawing|BeginSubtree)DisplayItems per client.
-void DisplayItemList::commitNewDisplayItems()
+//
+// TODO(pdr): Implement the DisplayListDiff algorithm for SlimmingPaintV2.
+void DisplayItemList::commitNewDisplayItems(DisplayListDiff*)
 {
     TRACE_EVENT2("blink,benchmark", "DisplayItemList::commitNewDisplayItems", "current_display_list_size", (int)m_currentDisplayItems.size(),
         "num_non_cached_new_items", (int)m_newDisplayItems.size() - m_numCachedItems);
@@ -381,13 +383,18 @@ void DisplayItemList::updateValidlyCachedClientsIfNeeded() const
     }
 }
 
-void DisplayItemList::commitNewDisplayItemsAndAppendToWebDisplayItemList(WebDisplayItemList* list)
+void DisplayItemList::appendToWebDisplayItemList(WebDisplayItemList* list)
 {
-    commitNewDisplayItems();
     for (const DisplayItem& item : m_currentDisplayItems)
         item.appendToWebDisplayItemList(list);
 }
 
+void DisplayItemList::commitNewDisplayItemsAndAppendToWebDisplayItemList(WebDisplayItemList* list)
+{
+    commitNewDisplayItems();
+    appendToWebDisplayItemList(list);
+}
+
 #if ENABLE(ASSERT)
 
 static void showUnderInvalidationError(const char* reason, const DisplayItem& displayItem)