Move assert.h/assert.cc from runtime/vm to runtime/platform

runtime/vm/zone.cc

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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 "vm/assert.h"
+#include "platform/assert.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
 #include "vm/os.h"
 #include "vm/utils.h"
 
 namespace dart {
 
 DEFINE_DEBUG_FLAG(bool, trace_zone_sizes,
                   false, "Traces allocation sizes in the zone.");
 
@@ skipping 219 matching lines @@
 
 void Zone::VisitObjectPointers(ObjectPointerVisitor* visitor) {
   Zone* zone = this;
   while (zone != NULL) {
     zone->handles()->VisitObjectPointers(visitor);
     zone = zone->previous_;
   }
 }
 
 }  // namespace dart