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

runtime/vm/os_linux.cc

Index: runtime/vm/os_linux.cc
diff --git a/runtime/vm/os_linux.cc b/runtime/vm/os_linux.cc
index 4917956ab1a556944ead4fe920d84fe26de901d8..b2233970892b68f3192fca09e4f39b0dd15668a9 100644
--- a/runtime/vm/os_linux.cc
+++ b/runtime/vm/os_linux.cc
@@ -1,7 +1,9 @@
-// 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/os.h"
+
 #include <errno.h>
 #include <limits.h>
 #include <time.h>
@@ -11,7 +13,6 @@
 #include <unistd.h>
 
 #include "vm/isolate.h"
-#include "vm/os.h"
 #include "vm/utils.h"
 
 namespace dart {