Introduce simple Thread class to support gradual refactoring of interfaces.

runtime/vm/zone.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/zone.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/flags.h"
 #include "vm/handles_impl.h"
 #include "vm/heap.h"
 #include "vm/isolate.h"
 #include "vm/os.h"
+#include "vm/thread.h"
 
 namespace dart {
 
 DEFINE_DEBUG_FLAG(bool, trace_zones,
                   false, "Traces allocation sizes in the zone.");
 
 
 // Zone segments represent chunks of memory: They have starting
 // address encoded in the this pointer and a size in bytes. They are
 // chained together to form the backing storage for an expanding zone.
@@ skipping 185 matching lines @@
   char* buffer = Alloc<char>(len + 1);
   va_list args2;
   va_start(args2, format);
   OS::VSNPrint(buffer, (len + 1), format, args2);
   va_end(args2);
 
   return buffer;
 }
 
 
+Zone* Zone::Current() {
+  return Thread::Current()->current_zone();
+}
+
 }  // namespace dart