Test infrastructure: Remove "race condition" bug from restarting batch process runners.

tools/testing/dart/test_runner.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Classes and methods for executing tests.
  *
  * This module includes:
  * - Managing parallel execution of tests, including timeout checks.
  * - Evaluating the output of each test as pass/fail/crash/timeout.
@@ skipping 717 matching lines @@
     _testStdout = [];
     _testStderr = [];
     _status = null;
     _stdoutDrained = false;
     _stderrDrained = false;
     _ignoreStreams = new MutableValue<bool>(false);  // Captured by closures.
     _stdoutStream.onLine = _readStdout(_stdoutStream, _testStdout);
     _stderrStream.onLine = _readStderr(_stderrStream, _testStderr);
     _timer = new Timer(testCase.timeout * 1000, _timeoutHandler);
     var line = _createArgumentsLine(testCase.batchTestArguments);
+    _process.stdin.onError = (err) {
+      print('Error on batch runner input stream stdin');
+      print('  Input line: $line');
+      print('  Previous test\'s status: $_status');
+      print('  Error: $err');
+      throw err;
+    };
     _process.stdin.write(line.charCodes());
   }
 
   String _createArgumentsLine(List<String> arguments) {
     return Strings.join(arguments, ' ').concat('\n');
   }
 
   void _reportResult() {
     if (!active) return;
     // _status == '>>> TEST {PASS, FAIL, OK, CRASH, FAIL, TIMEOUT}'
@@ skipping 90 matching lines @@
         while (line != null) {
           _testStderr.add(line);
           line = _stderrStream.readLine();
         }
         _stderrDrained = true;
         _stdoutDrained = true;
         _process.close();
         _startProcess(() { _reportResult(); });
       } else {  // No active test case running.
         _process.close();
-        _startProcess(() { });
+        _process = null;
       }
     };
-  } 
+  }
 
-  void _timeoutHandler(ignore) { 
+  void _timeoutHandler(ignore) {
     _process.onExit = makeExitHandler(">>> TEST TIMEOUT");
     _process.kill();
   }
 
   void _startProcess(then) {
     _process = Process.start(_executable, _batchArguments);
     _stdoutStream = new StringInputStream(_process.stdout);
     _stderrStream = new StringInputStream(_process.stderr);
     _process.onExit = makeExitHandler(">>> TEST CRASH");
     _process.onError = (e) {
@@ skipping 306 matching lines @@
         // the developer doesn't waste his or her time trying to fix a bunch of
         // tests that appear to be broken but were actually just flakes that
         // didn't get retried because there had already been one failure.
         bool allowRetry = _MAX_FAILED_NO_RETRY > _progress.numFailedTests;
         new RunningProcess(test, allowRetry, this).start();
       }
       _numProcesses++;
     }
   }
 }