[heap] User safer root set accessor when possible.

src/objects-debug.cc

Index: src/objects-debug.cc
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index 93da2ed3874960606958888ae0255eaf00745a4a..961ad51f61bd9a05407a3b39914f15d9e8fba740 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -1236,7 +1236,8 @@ bool CanLeak(Object* obj, Heap* heap, bool skip_weak_cell) {
   if (obj->IsMap()) {
     Map* map = Map::cast(obj);
     for (int i = 0; i < Heap::kStrongRootListLength; i++) {
-      if (map == heap->roots_array_start()[i]) return false;
+      Heap::RootListIndex root_index = static_cast<Heap::RootListIndex>(i);
+      if (map == heap->root(root_index)) return false;
     }
     return true;
   }