Reintroduce runtime zone to Isolate.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index fec3dc66ab4260b63b6e8a6023d34961e53536bc..3a6f140506df0ecb430eb8df0ebc56c346870814 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1762,6 +1762,7 @@ Isolate::Isolate()
       descriptor_lookup_cache_(NULL),
       handle_scope_implementer_(NULL),
       unicode_cache_(NULL),
+      runtime_zone_(this),
       in_use_list_(0),
       free_list_(0),
       preallocated_storage_preallocated_(false),
@@ -1960,6 +1961,9 @@ 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,
   // except for the default isolate, where it can
   // still contain up to one entry stack item