Disable optimization in r20548 to make bots green again.

runtime/vm/intermediate_language.cc

 // Copyright (c) 2013, 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/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 511 matching lines @@
   ASSERT(this != other);
 
   Value* current = NULL;
   Value* next = input_use_list();
   if (next != NULL) {
     // Change all the definitions.
     while (next != NULL) {
       current = next;
       current->set_definition(other);
       // Do not discard some useful inferred types.
-      if (current->Type() == this->Type()) {
-        current->SetReachingType(NULL);
-      }
+      // TODO(srdjan): Enable once checked mode issues investigated.
+      // if (current->Type() == this->Type()) {
+      //   current->SetReachingType(NULL);
+      // }
       next = current->next_use();
     }
 
     // Concatenate the lists.
     next = other->input_use_list();
     current->set_next_use(next);
     if (next != NULL) next->set_previous_use(current);
     other->set_input_use_list(input_use_list());
     set_input_use_list(NULL);
   }
@@ skipping 1797 matching lines @@
     default:
       UNREACHABLE();
   }
   return kPowRuntimeEntry;
 }
 
 
 #undef __
 
 }  // namespace dart