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

runtime/vm/handles.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/handles.h"
 
-#include "vm/assert.h"
+#include "platform/assert.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
 #include "vm/os.h"
 #include "vm/raw_object.h"
 #include "vm/utils.h"
 #include "vm/visitor.h"
 #include "vm/zone.h"
 
 #include "vm/handles_impl.h"
 
@@ skipping 84 matching lines @@
   isolate->IncrementNoHandleScopeDepth();
 }
 
 
 NoHandleScope::~NoHandleScope() {
   isolate()->DecrementNoHandleScopeDepth();
 }
 #endif  // defined(DEBUG)
 
 }  // namespace dart