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

runtime/vm/heap.cc

Index: runtime/vm/heap.cc
diff --git a/runtime/vm/heap.cc b/runtime/vm/heap.cc
index f625256c8fea8371c876f917f0b18435bba3ea94..76b343928d4ad1f56bf337766b56f08522c78e3d 100644
--- a/runtime/vm/heap.cc
+++ b/runtime/vm/heap.cc
@@ -1,10 +1,10 @@
-// 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/heap.h"
 
-#include "vm/assert.h"
+#include "platform/assert.h"
 #include "vm/compiler_stats.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"