Fix break on unhandled exception

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 357 matching lines @@
         break;
       }
     }
   }
   return token_pos_;
 }
 
 
 intptr_t ActivationFrame::TryIndex() {
   if (desc_rec_ == NULL) {
+    TokenPos();  // Side effect: compute desc_rec_ lazily.
+  }
+  if (desc_rec_ == NULL) {
     return -1;
   } else {
     return desc_rec_->try_index();
   }
 }
 
 
 intptr_t ActivationFrame::LineNumber() {
   // Compute line number lazily since it causes scanning of the script.
   if ((line_number_ < 0) && (TokenPos() >= 0)) {
@@ skipping 2187 matching lines @@
 }
 
 
 void Debugger::RegisterCodeBreakpoint(CodeBreakpoint* bpt) {
   ASSERT(bpt->next() == NULL);
   bpt->set_next(code_breakpoints_);
   code_breakpoints_ = bpt;
 }
 
 }  // namespace dart