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

runtime/vm/virtual_memory_macos.cc

Index: runtime/vm/virtual_memory_macos.cc
diff --git a/runtime/vm/virtual_memory_macos.cc b/runtime/vm/virtual_memory_macos.cc
index 0cf2dadc9d0c156564d76cffa90f460e58d11801..0d3f876f3d51fca2245eae7e7f9fb65ddd29ec19 100644
--- a/runtime/vm/virtual_memory_macos.cc
+++ b/runtime/vm/virtual_memory_macos.cc
@@ -1,12 +1,13 @@
-// 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/virtual_memory.h"
+
 #include <sys/mman.h>
 #include <unistd.h>
 
-#include "vm/virtual_memory.h"
-#include "vm/assert.h"
+#include "platform/assert.h"
 #include "vm/utils.h"
 
 namespace dart {