Fix optimizer bug with external strings.

runtime/vm/redundancy_elimination.cc

 // Copyright (c) 2016, 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/redundancy_elimination.h"
 
 #include "vm/bit_vector.h"
 #include "vm/flow_graph.h"
 #include "vm/hash_map.h"
 #include "vm/il_printer.h"
@@ skipping 532 matching lines @@
         RepresentationBits::encode(rep) |
         ElementSizeBits::encode(scale);
   }
 
   static ElementSize ElementSizeFor(intptr_t class_id) {
     switch (class_id) {
       case kArrayCid:
       case kImmutableArrayCid:
       case kOneByteStringCid:
       case kTwoByteStringCid:
+      case kExternalOneByteStringCid:
+      case kExternalTwoByteStringCid:
         // Object arrays and strings do not allow accessing them through
         // different types. No need to attach scale.
         return kNoSize;
 
       case kTypedDataInt8ArrayCid:
       case kTypedDataUint8ArrayCid:
       case kTypedDataUint8ClampedArrayCid:
       case kExternalTypedDataUint8ArrayCid:
       case kExternalTypedDataUint8ClampedArrayCid:
         return kInt8;
@@ skipping 2900 matching lines @@
         join->phis_ = NULL;
       } else {
         join->phis_->TruncateTo(to_index);
       }
     }
   }
 }
 
 
 }  // namespace dart