When a catch is unreachable, use the canonical empty array instead of null as its type array.

runtime/vm/object.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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 11648 matching lines @@
 
 bool ExceptionHandlers::HasCatchAll(intptr_t try_index) const {
   ASSERT((try_index >= 0) && (try_index < num_entries()));
   return raw_ptr()->data()[try_index].has_catch_all;
 }
 
 
 void ExceptionHandlers::SetHandledTypes(intptr_t try_index,
                                         const Array& handled_types) const {
   ASSERT((try_index >= 0) && (try_index < num_entries()));
+  ASSERT(!handled_types.IsNull());
   const Array& handled_types_data =
       Array::Handle(raw_ptr()->handled_types_data_);
   handled_types_data.SetAt(try_index, handled_types);
 }
 
 
 RawArray* ExceptionHandlers::GetHandledTypes(intptr_t try_index) const {
   ASSERT((try_index >= 0) && (try_index < num_entries()));
   Array& array = Array::Handle(raw_ptr()->handled_types_data_);
   array ^= array.At(try_index);
@@ skipping 10021 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart