Fix exit code handling for Android testing.

tools/testing/dart/android.dart

 // 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.
 
 library android;
 
 import "dart:async";
 import "dart:convert" show LineSplitter, UTF8;
 import "dart:core";
 import "dart:collection";
@@ skipping 315 matching lines @@
     int exitCode = result.exitCode;
     var lines = result
         .stdout.split('\n')
         .where((line) => line.trim().length > 0)
         .toList();
     if (lines.length > 0) {
       int index = lines.last.indexOf(MARKER);
       if (index >= 0) {
         exitCode = int.parse(
             lines.last.substring(index + MARKER.length).trim());
-        exitCode = exitCode.toSigned(8);
+        if (exitCode > 128 && exitCode <= 128 + 31) {
+          // Return negative exit codes for signals 1..31 (128+N for signal N)
+          exitCode = 128 - exitCode;
+        }
       } else {
         // In case of timeouts, for example, we won't get the exitcode marker.
         assert(result.exitCode != 0);
       }
     }
     return new AdbCommandResult(
         result.command, result.stdout, result.stderr, exitCode,
         result.timedOut);
   }
 
@@ skipping 80 matching lines @@
 
   void releaseDevice(AdbDevice device) {
     if (_waiter.length > 0) {
       Completer completer = _waiter.removeFirst();
       completer.complete(device);
     } else {
       _idleDevices.add(device);
     }
   }
 }