Remove deprecated_internalProblem.

pkg/front_end/lib/src/fasta/command_line.dart

 // 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.
 
 library fasta.command_line;
 
 import 'fasta_codes.dart' show Message, templateFastaCLIArgumentRequired;
 
-import 'deprecated_problems.dart'
-    show deprecated_inputError, deprecated_internalProblem;
+import 'deprecated_problems.dart' show deprecated_inputError;
+
+import 'problems.dart' show unhandled;
 
 deprecated_argumentError(Message usage, String message) {
   if (usage != null) print(usage.message);
   deprecated_inputError(null, null, message);
 }
 
 argumentError(Message usage, Message message) {
   if (usage != null) print(usage.message);
   deprecated_inputError(null, null, message.message);
 }
@@ skipping 138 matching lines @@
                 parsedValue = Uri.base.resolve(value);
               } else if (valueSpecification == String) {
                 parsedValue = value;
               } else if (valueSpecification is String) {
                 return deprecated_argumentError(
                     usage,
                     "Unrecognized value specification: "
                     "'$valueSpecification', try using a type literal instead.");
               } else {
                 // All possible cases should have been handled above.
-                return deprecated_internalProblem("assertion failure");
+                return unhandled("${valueSpecification.runtimeType}",
+                    "CommandLine.parse", -1, null);
               }
               result.options[argument] = parsedValue;
               break;
 
             default:
               return deprecated_argumentError(usage,
                   "Unrecognized value specification: '$valueSpecification'.");
           }
         }
       } else if (argument == "/?" || argument == "/h") {
         result.options[argument] = true;
       } else {
         result.arguments.add(argument);
       }
     }
     result.arguments.addAll(nonOptions);
     return result;
   }
 }