Don't return negative token positions in stack traces.

runtime/vm/debugger.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/debugger.h"
 
 #include "include/dart_api.h"
 
 #include "vm/code_generator.h"
 #include "vm/code_patcher.h"
@@ skipping 1032 matching lines @@
                     line,
                     ctx_.ToCString(),
                     ContextLevel());
 }
 
 
 void ActivationFrame::PrintToJSONObject(JSONObject* jsobj,
                                         bool full) {
   const Script& script = Script::Handle(SourceScript());
   jsobj->AddProperty("type", "Frame");
-  jsobj->AddLocation(script, TokenPos());
+  TokenPosition pos = TokenPos();
+  if (pos.IsSynthetic()) {
+    pos = pos.FromSynthetic();
+  }
+  jsobj->AddLocation(script, pos);
   jsobj->AddProperty("function", function(), !full);
   jsobj->AddProperty("code", code());
   if (full) {
     // TODO(cutch): The old "full" script usage no longer fits
     // in the world where we pass the script as part of the
     // location.
     jsobj->AddProperty("script", script, !full);
   }
   {
     JSONArray jsvars(jsobj, "vars");
@@ skipping 2258 matching lines @@
 
 void Debugger::RegisterCodeBreakpoint(CodeBreakpoint* bpt) {
   ASSERT(bpt->next() == NULL);
   bpt->set_next(code_breakpoints_);
   code_breakpoints_ = bpt;
 }
 
 #endif  // !PRODUCT
 
 }  // namespace dart