Change age-mark to not expect pages to be in increasing order.

src/heap-inl.h

Index: src/heap-inl.h
diff --git a/src/heap-inl.h b/src/heap-inl.h
index dfff41831a9ec537e7607ea3e5c468ec55ccdc95..2b432c049c56119a493810134d90f12fb9f66b63 100644
--- a/src/heap-inl.h
+++ b/src/heap-inl.h
@@ -292,9 +292,12 @@ bool Heap::ShouldBePromoted(Address old_address, int object_size) {
   // An object should be promoted if:
   // - the object has survived a scavenge operation or
   // - to space is already 25% full.
-  // TODO(gc): Do something about age-mark in paged new-space.
-  return old_address < new_space_.age_mark()
-      || (new_space_.Size() + object_size) >= (new_space_.Capacity() >> 2);
+  NewSpacePage* page = NewSpacePage::FromAddress(old_address);
+  Address age_mark = new_space_.age_mark();
+  bool below_mark = page->IsFlagSet(MemoryChunk::NEW_SPACE_BELOW_AGE_MARK) &&
+      (!page->ContainsLimit(age_mark) || old_address < age_mark);
+  return below_mark ||
+      (new_space_.Size() + object_size) >= (new_space_.Capacity() >> 2);
 }