Split dart_api.h into multiple parts:

runtime/vm/dart_api_message.h

 // 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.
 
 #ifndef VM_DART_API_MESSAGE_H_
 #define VM_DART_API_MESSAGE_H_
 
+#include "include/dart_native_api.h"
 #include "vm/dart_api_state.h"
 #include "vm/snapshot.h"
 
 namespace dart {
 
 // Use this C structure for reading internal objects in the serialized
 // data. These are objects that we need to process in order to
 // generate the Dart_CObject graph but that we don't want to expose in
 // that graph.
 struct Dart_CObject_Internal : public Dart_CObject {
@@ skipping 165 matching lines @@
   Dart_CObject** forward_list_;
   intptr_t forward_list_length_;
   intptr_t forward_id_;
 
   DISALLOW_COPY_AND_ASSIGN(ApiMessageWriter);
 };
 
 }  // namespace dart
 
 #endif  // VM_DART_API_MESSAGE_H_