Replaced different means of zone pooling/reusing by one zone segment pool

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 4dcec2750faa7a1f1d3f99c45d58665667fe897b..3c9123c6a164b38279d8f71dc206dddb35a75c52 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1972,7 +1972,6 @@ Isolate::Isolate(bool enable_serializer)
       allocator_(FLAG_trace_gc_object_stats
                      ? new VerboseAccountingAllocator(&heap_, 256 * KB)
                      : new AccountingAllocator()),
-      runtime_zone_(new Zone(allocator_)),
       inner_pointer_to_code_cache_(NULL),
       global_handles_(NULL),
       eternal_handles_(NULL),
@@ -2245,9 +2244,6 @@ Isolate::~Isolate() {
   delete cancelable_task_manager_;
   cancelable_task_manager_ = nullptr;
 
-  delete runtime_zone_;
-  runtime_zone_ = nullptr;
-
   delete allocator_;
   allocator_ = nullptr;