Fix bug on arm64.

tools/testing/dart/runtime_configuration.dart

 // 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.
 
 library runtime_configuration;
 
 import 'compiler_configuration.dart' show
     CommandArtifact;
 
 // TODO(ahe): Remove this import, we can precompute all the values required
@@ skipping 153 matching lines @@
   int computeTimeoutMultiplier({
       bool isDebug: false,
       bool isChecked: false,
       String arch}) {
     int multiplier = 1;
     switch (arch) {
       case 'simarm':
       case 'arm':
       case 'simmips':
       case 'mips':
+      case 'simarm64':
         multiplier *= 4;
         break;
     }
     if (isDebug) {
       multiplier *= 2;
     }
     return multiplier;
   }
 }
 
@@ skipping 37 matching lines @@
 class DummyRuntimeConfiguration extends DartVmRuntimeConfiguration {
   List<Command> computeRuntimeCommands(
       TestSuite suite,
       CommandBuilder commandBuilder,
       CommandArtifact artifact,
       List<String> arguments,
       Map<String, String> environmentOverrides) {
     throw "Unimplemented runtime '$runtimeType'";
   }
 }