Make top and limit field in AllocationInfo private, assert on non-aligned setting of these fields, …

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 944bfa6232ee9d5704d2b5c3b587c41727bb9f00..bbd95ce7232d49b13547a197221e9f5a5038a34f 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -9156,7 +9156,7 @@ Handle<String> SeqString::Truncate(Handle<SeqString> string, int new_length) {
   if (newspace->Contains(start_of_string) &&
       newspace->top() == start_of_string + old_size) {
     // Last allocated object in new space.  Simply lower allocation top.
-    *(newspace->allocation_top_address()) = start_of_string + new_size;
+    newspace->set_top(start_of_string + new_size);
   } else {
     // Sizes are pointer size aligned, so that we can use filler objects
     // that are a multiple of pointer size.