Support use of external strings as inputs to LoadCodeUnitsInstr.

runtime/vm/flow_graph_range_analysis.cc

 // Copyright (c) 2014, 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_range_analysis.h"
 
 #include "vm/bit_vector.h"
 #include "vm/il_printer.h"
 
 namespace dart {
@@ skipping 2886 matching lines @@
                      RangeBoundary::FromConstant(0xFFFF));
       break;
     default:
       Definition::InferRange(analysis, range);
       break;
   }
 }
 
 
 void LoadCodeUnitsInstr::InferRange(RangeAnalysis* analysis, Range* range) {
-  ASSERT(class_id() == kOneByteStringCid ||
-         class_id() == kTwoByteStringCid);
+  ASSERT(RawObject::IsStringClassId(class_id()));
   switch (class_id()) {
     case kOneByteStringCid:
     case kTwoByteStringCid:
+    case kExternalOneByteStringCid:
+    case kExternalTwoByteStringCid:
       *range = Range(RangeBoundary::FromConstant(0),
                      RangeBoundary::FromConstant(kMaxUint32));
       break;
     default:
       UNREACHABLE();
       break;
   }
 }
 
 
@@ skipping 222 matching lines @@
     }
   } while (CanonicalizeMaxBoundary(&max) ||
            CanonicalizeMinBoundary(&canonical_length));
 
   // Failed to prove that maximum is bounded with array length.
   return false;
 }
 
 
 }  // namespace dart