Reland of "🏄 [heap] Add page evacuation mode for new->old"

src/heap/spaces-inl.h

Index: src/heap/spaces-inl.h
diff --git a/src/heap/spaces-inl.h b/src/heap/spaces-inl.h
index db01d0eed99e81690f0e15516b56096fd64de20f..3213d17c136cc024f8d12851575bd3b7d8e3c195 100644
--- a/src/heap/spaces-inl.h
+++ b/src/heap/spaces-inl.h
@@ -287,6 +287,7 @@ NewSpacePage* NewSpacePage::Initialize(Heap* heap, MemoryChunk* chunk,
 // --------------------------------------------------------------------------
 // PagedSpace
 
+template <Page::InitializationMode mode>
 Page* Page::Initialize(Heap* heap, MemoryChunk* chunk, Executability executable,
                        PagedSpace* owner) {
   Page* page = reinterpret_cast<Page*>(chunk);
@@ -299,11 +300,25 @@ Page* Page::Initialize(Heap* heap, MemoryChunk* chunk, Executability executable,
 
   // Make sure that categories are initialized before freeing the area.
   page->InitializeFreeListCategories();
-  owner->Free(page->area_start(), page->area_size());
+  // In the case we do not free the memory, we effectively account for the whole
+  // page as allocated memory that cannot be used for further allocations.
+  if (mode == kFreeMemory) {
+    owner->Free(page->area_start(), page->area_size());
+  }
 
   return page;
 }
 
+Page* Page::Convert(NewSpacePage* old_page, PagedSpace* new_owner) {
+  old_page->set_owner(new_owner);
+  old_page->SetFlags(0, ~0);
+  new_owner->AccountCommitted(old_page->size());
+  Page* new_page = Page::Initialize<kDoNotFreeMemory>(
+      old_page->heap(), old_page, NOT_EXECUTABLE, new_owner);
+  new_page->InsertAfter(new_owner->anchor()->prev_page());
+  return new_page;
+}
+
 void Page::InitializeFreeListCategories() {
   for (int i = kFirstCategory; i < kNumberOfCategories; i++) {
     categories_[i].Initialize(static_cast<FreeListCategoryType>(i));