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 fd2876684d42610a9f7e114fc70a98dfbb5f67ee..159e7a900f52b9a26f351b4b33d7e240b18f8e8d 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),
@@ -2169,9 +2168,6 @@ void Isolate::SetIsolateThreadLocals(Isolate* isolate,
 Isolate::~Isolate() {
   TRACE_ISOLATE(destructor);
 
-  // Has to be called while counters_ are still alive
-  runtime_zone_->DeleteKeptSegment();
-
   // The entry stack must be empty when we get here.
   DCHECK(entry_stack_ == NULL || entry_stack_->previous_item == NULL);
 
@@ -2248,9 +2244,6 @@ Isolate::~Isolate() {
   delete cancelable_task_manager_;
   cancelable_task_manager_ = nullptr;
 
-  delete runtime_zone_;
-  runtime_zone_ = nullptr;
-
   delete allocator_;
   allocator_ = nullptr;