Subtree caching implementation in blink-core

Source/core/layout/LayoutBlock.cpp

Index: Source/core/layout/LayoutBlock.cpp
diff --git a/Source/core/layout/LayoutBlock.cpp b/Source/core/layout/LayoutBlock.cpp
index 116c979367c9b7c7fc0eb820d6eeff761531ee70..b21c7dab351efadb41b54cd017833cfdbb46e521 100644
--- a/Source/core/layout/LayoutBlock.cpp
+++ b/Source/core/layout/LayoutBlock.cpp
@@ -368,13 +368,24 @@ inline static void invalidateDisplayItemClientForStartOfContinuationsIfNeeded(co
         startOfContinuations->invalidateDisplayItemClient(*startOfContinuations);
 }
 
-void LayoutBlock::invalidateDisplayItemClients(const LayoutBoxModelObject& paintInvalidationContainer) const
+void LayoutBlock::invalidateDisplayItemClients(const LayoutBoxModelObject& paintInvalidationContainer)
 {
     LayoutBox::invalidateDisplayItemClients(paintInvalidationContainer);
     ASSERT(RuntimeEnabledFeatures::slimmingPaintEnabled());
     invalidateDisplayItemClientForStartOfContinuationsIfNeeded(*this);
 }
 
+void LayoutBlock::clearRepaintFlagsOfSubtrees()
+{
+    LayoutBox::clearRepaintFlagsOfSubtrees();
+    // TODO(wangxianzhu): We should traverse in painting order instead of positioning order.
+    // See comments in LayoutObject::markContainerChainForChildNeedsRepaint.
+    if (TrackedLayoutBoxListHashSet* positionedObjects = this->positionedObjects()) {
+        for (auto o : *positionedObjects)
+            o->clearRepaintFlagsRecursively();
+    }
+}
+
 void LayoutBlock::addChildIgnoringContinuation(LayoutObject* newChild, LayoutObject* beforeChild)
 {
     if (beforeChild && beforeChild->parent() != this) {