Fix compilation failure caused by r38404.

runtime/vm/flow_graph_optimizer.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/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/cpu.h"
 #include "vm/dart_entry.h"
@@ skipping 6098 matching lines @@
     InsertAlias(Place::CreateAnyInstanceAnyIndexAlias(isolate_,
         kAnyInstanceAnyIndexAlias));
     for (intptr_t i = 0; i < places_.length(); i++) {
       AddRepresentative(places_[i]);
     }
     ComputeKillSets();
   }
 
   intptr_t LookupAliasId(const Place& alias) {
     const Place* result = aliases_map_.Lookup(&alias);
-    return (result != NULL) ? result->id() : kNoAlias;
+    return (result != NULL) ? result->id() : static_cast<intptr_t>(kNoAlias);
   }
 
   bool IsStore(Instruction* instr, BitVector** killed) {
     bool is_load = false, is_store = false;
     Place place(instr, &is_load, &is_store);
     if (is_store && (place.kind() != Place::kNone)) {
       const intptr_t alias_id = LookupAliasId(place.ToAlias());
       if (alias_id != kNoAlias) {
         *killed = GetKilledSet(alias_id);
       }
@@ skipping 4287 matching lines @@
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits_collector_.exits().length(); i++) {
     CreateMaterializationAt(
         exits_collector_.exits()[i], alloc, alloc->cls(), *slots);
   }
 }
 
 
 }  // namespace dart