Fix for issue 9617, throw a snapshot write error when encountering stacktrace objects instead of an…

runtime/vm/raw_object_snapshot.cc

 // 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/bigint_operations.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/snapshot.h"
 #include "vm/symbols.h"
 #include "vm/visitor.h"
@@ skipping 2496 matching lines @@
     // Write out the class and tags information.
     writer->WriteIndexedObject(kStacktraceCid);
     writer->WriteIntptrValue(writer->GetObjectTags(this));
 
     // There are no non object pointer fields.
 
     // Write out all the object pointer fields.
     SnapshotWriterVisitor visitor(writer);
     visitor.VisitPointers(from(), to());
   } else {
-    UNREACHABLE();  // Stacktraces are not supported for other snapshot forms.
+    // Stacktraces are not allowed in other snapshot forms.
+    writer->SetWriteException(Exceptions::kArgument,
+                              "Illegal argument in isolate message"
+                              " : (object is a stacktrace)");
   }
 }
 
 
 RawJSRegExp* JSRegExp::ReadFrom(SnapshotReader* reader,
                                 intptr_t object_id,
                                 intptr_t tags,
                                 Snapshot::Kind kind) {
   ASSERT(reader != NULL);
   ASSERT(kind == Snapshot::kMessage);
@@ skipping 81 matching lines @@
   // Write out the class and tags information.
   writer->WriteIndexedObject(kWeakPropertyCid);
   writer->WriteIntptrValue(writer->GetObjectTags(this));
 
   // Write out all the other fields.
   writer->Write<RawObject*>(ptr()->key_);
   writer->Write<RawObject*>(ptr()->value_);
 }
 
 }  // namespace dart