Get rid of ZoneScope completely.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index b1e2b07835e2a781988ccd3ac5d0c6a1c78712fe..e6f41691d0aab81d9faacc67b23bc0622342df96 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -892,7 +892,6 @@ class Isolate {
     ASSERT(handle_scope_implementer_);
     return handle_scope_implementer_;
   }
-  Zone* runtime_zone() { return &runtime_zone_; }
 
   UnicodeCache* unicode_cache() {
     return unicode_cache_;
@@ -1260,7 +1259,6 @@ class Isolate {
   v8::ImplementationUtilities::HandleScopeData handle_scope_data_;
   HandleScopeImplementer* handle_scope_implementer_;
   UnicodeCache* unicode_cache_;
-  Zone runtime_zone_;
   PreallocatedStorage in_use_list_;
   PreallocatedStorage free_list_;
   bool preallocated_storage_preallocated_;