Remove a major source of flaky service test failures.

runtime/observatory/tests/service/test_helper.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 test_helper;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'package:observatory/service_io.dart';
@@ skipping 263 matching lines @@
             List<String> extraArgs,
             List<VMTest> vmTests,
             List<IsolateTest> isolateTests,
             bool pause_on_start: false,
             bool pause_on_exit: false,
             bool verbose_vm: false,
             bool pause_on_unhandled_exceptions: false,
             bool testeeControlsServer: false,
             bool useAuthToken: false}) {
     var process = new _ServiceTesteeLauncher();
+    bool testsDone = false;
     process.launch(pause_on_start, pause_on_exit,
                    pause_on_unhandled_exceptions,
                    testeeControlsServer,
                    useAuthToken, extraArgs).then((Uri serverAddress) async {
       if (mainArgs.contains("--gdb")) {
         var pid = process.process.pid;
         var wait = new Duration(seconds: 10);
         print("Testee has pid $pid, waiting $wait before continuing");
         sleep(wait);
       }
@@ skipping 24 matching lines @@
           var testIndex = 1;
           var totalTests = isolateTests.length;
           for (var test in isolateTests) {
             vm.verbose = verbose_vm;
             print('Running $name [$testIndex/$totalTests]');
             testIndex++;
             await test(isolate);
           }
         }
 
+        print('All service tests completed successfully.');
+        testsDone = true;
         await process.requestExit();
       }, onError: (error, stackTrace) {
-        process.requestExit();
-        print('Unexpected exception in service tests: $error\n$stackTrace');
-        throw error;
+        if (testsDone) {
+          print('Ignoring late exception during process exit:\n'
+                '$error\n#stackTrace');
+        } else {
+          process.requestExit();
+          print('Unexpected exception in service tests: $error\n$stackTrace');
+          throw error;
+        }
       });
     });
   }
 }
 
 /// Runs [tests] in sequence, each of which should take an [Isolate] and
 /// return a [Future]. Code for setting up state can run before and/or
 /// concurrently with the tests. Uses [mainArgs] to determine whether
 /// to run tests or testee in this invokation of the script.
 Future runIsolateTests(List<String> mainArgs,
@@ skipping 86 matching lines @@
     new _ServiceTesterRunner().run(
         mainArgs: mainArgs,
         extraArgs: extraArgs,
         vmTests: tests,
         pause_on_start: pause_on_start,
         pause_on_exit: pause_on_exit,
         verbose_vm: verbose_vm,
         pause_on_unhandled_exceptions: pause_on_unhandled_exceptions);
   }
 }