Support initialized mixin fields across scripts

runtime/vm/datastream.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_DATASTREAM_H_
 #define VM_DATASTREAM_H_
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/allocation.h"
@@ skipping 11 matching lines @@
 
 typedef uint8_t* (*ReAlloc)(uint8_t* ptr, intptr_t old_size, intptr_t new_size);
 
 // Stream for reading various types from a buffer.
 class ReadStream : public ValueObject {
  public:
   ReadStream(const uint8_t* buffer, intptr_t size) : buffer_(buffer),
                                                      current_(buffer),
                                                      end_(buffer + size)  {}
 
+  void SetStream(const uint8_t* buffer, intptr_t size) {
+    buffer_ = buffer;
+    current_ = buffer;
+    end_ = buffer + size;
+  }
+
   template<int N, typename T>
   class Raw { };
 
   template<typename T>
   class Raw<1, T> {
    public:
     static T Read(ReadStream* st) {
       return bit_cast<T>(st->ReadByte());
     }
   };
@@ skipping 205 matching lines @@
   intptr_t current_size_;
   ReAlloc alloc_;
   intptr_t increment_size_;
 
   DISALLOW_COPY_AND_ASSIGN(WriteStream);
 };
 
 }  // namespace dart
 
 #endif  // VM_DATASTREAM_H_