Disable display item caching

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 f4723e3b27c2f291c80104e8df8da8ae8adc2f5c..c2b800adb3cf2a7c2a151624e4769053f4c8d3ff 100644
--- a/Source/platform/graphics/paint/DisplayItemList.cpp
+++ b/Source/platform/graphics/paint/DisplayItemList.cpp
@@ -18,8 +18,7 @@ namespace blink {
 const PaintList& DisplayItemList::paintList()
 {
     ASSERT(RuntimeEnabledFeatures::slimmingPaintEnabled());
-
-    updatePaintList();
+    ASSERT(m_newPaints.isEmpty());
     return m_paintList;
 }
 
@@ -44,6 +43,11 @@ void DisplayItemList::invalidateAll()
     m_cachedClients.clear();
 }
 
+bool DisplayItemList::clientCacheIsValid(DisplayItemClient client) const
+{
+    return RuntimeEnabledFeatures::slimmingPaintDisplayItemCacheEnabled() && m_cachedClients.contains(client);
+}
+
 PaintList::iterator DisplayItemList::findNextMatchingCachedItem(PaintList::iterator begin, const DisplayItem& displayItem)
 {
     PaintList::iterator end = m_paintList.end();
@@ -74,6 +78,13 @@ static void appendDisplayItem(PaintList& list, HashSet<DisplayItemClient>& clien
 // the ordering implied by the existing paint list, extra treewalks are avoided.
 void DisplayItemList::updatePaintList()
 {
+    if (!RuntimeEnabledFeatures::slimmingPaintDisplayItemCacheEnabled()) {
+        m_paintList.clear();
+        m_paintList.swap(m_newPaints);
+        m_cachedClients.clear();
+        return;
+    }
+
     PaintList updatedList;
     HashSet<DisplayItemClient> newCachedClients;