Keep zone cached in SnapshotReader to allow removing ZoneHandle(Isolate*) interface.

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 6639 matching lines @@
         a.SetAt(count++, *deopt_id_to_ic_data[i]);
       }
     }
     set_ic_data_array(a);
   }
 }
 
 
 void Function::RestoreICDataMap(
     ZoneGrowableArray<const ICData*>* deopt_id_to_ic_data) const {
-  Isolate* isolate = Isolate::Current();
-  const Array& saved_icd = Array::Handle(isolate, ic_data_array());
+  Zone* zone = Thread::Current()->zone();
+  const Array& saved_icd = Array::Handle(zone, ic_data_array());
   if (saved_icd.Length() == 0) {
     deopt_id_to_ic_data->Clear();
     return;
   }
   ICData& icd = ICData::Handle();
   icd ^= saved_icd.At(saved_icd.Length() - 1);
   const intptr_t len = icd.deopt_id() + 1;
   deopt_id_to_ic_data->SetLength(len);
   for (intptr_t i = 0; i < len; i++) {
     (*deopt_id_to_ic_data)[i] = NULL;
   }
   for (intptr_t i = 0; i < saved_icd.Length(); i++) {
-    ICData& icd = ICData::ZoneHandle(isolate);
+    ICData& icd = ICData::ZoneHandle(zone);
     icd ^= saved_icd.At(i);
     (*deopt_id_to_ic_data)[icd.deopt_id()] = &icd;
   }
 }
 
 
 void Function::set_ic_data_array(const Array& value) const {
   StorePointer(&raw_ptr()->ic_data_array_, value.raw());
 }
 
@@ skipping 14069 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart