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

runtime/vm/service_test.cc

 // Copyright (c) 2013, 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 "platform/globals.h"
 
 #include "include/dart_debugger_api.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
@@ skipping 17 matching lines @@
   ~ServiceTestMessageHandler() {
     free(_msg);
   }
 
   bool HandleMessage(Message* message) {
     if (_msg != NULL) {
       free(_msg);
     }
 
     // Parse the message.
-    SnapshotReader reader(message->data(), message->len(),
-                          Snapshot::kMessage, Isolate::Current());
+    SnapshotReader reader(message->data(), message->len(), Snapshot::kMessage,
+                          Isolate::Current(), Thread::Current()->zone());
     const Object& response_obj = Object::Handle(reader.ReadObject());
     String& response = String::Handle();
     response ^= response_obj.raw();
     _msg = strdup(response.ToCString());
     return true;
   }
 
   // Removes a given json key:value from _msg.
   void filterMsg(const char* key) {
     int key_len = strlen(key);
@@ skipping 1422 matching lines @@
       Eval(lib, "[0, port, 'getCpuProfile', ['tags'], ['Bogus']]");
   Service::HandleIsolateMessage(isolate, service_msg);
   handler.HandleNextMessage();
   // Expect error.
   EXPECT_SUBSTRING("\"type\":\"Error\"", handler.msg());
 }
 
 #endif  // !defined(TARGET_ARCH_ARM64)
 
 }  // namespace dart