Support initialized mixin fields across scripts

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 20386)
+++ runtime/vm/object.cc	(working copy)
@@ -5349,7 +5349,7 @@
 
 
 TokenStream::Iterator::Iterator(const TokenStream& tokens, intptr_t token_pos)
-    : tokens_(tokens),
+    : tokens_(TokenStream::Handle(tokens.raw())),
       data_(ExternalUint8Array::Handle(tokens.GetStream())),
       stream_(data_.ByteAddr(0), data_.Length()),
       token_objects_(Array::Handle(tokens.TokenObjects())),
@@ -5361,6 +5361,20 @@
 }
 
 
+void TokenStream::Iterator::SetStream(const TokenStream& tokens,
+                                      intptr_t token_pos) {
+  tokens_ = tokens.raw();
+  data_ = tokens.GetStream();
+  stream_.SetStream(data_.ByteAddr(0), data_.Length());
+  token_objects_ = tokens.TokenObjects();
+  obj_ = Object::null();
+  cur_token_pos_ = token_pos;
+  cur_token_kind_ = Token::kILLEGAL;
+  cur_token_obj_index_ = -1;
+  SetCurrentPosition(token_pos);
+}
+
+
 bool TokenStream::Iterator::IsValid() const {
   return !tokens_.IsNull();
 }