Fix a race condition in BrowserManager. (#490)

If a web test emitted any kind of message after the browser manager was
closed, the debugging timer would reset and cause the VM not to exit for
an extra three seconds.

Author: nex3

CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.12.15+12
+
+* Fix a race condition that could cause the runner to stall for up to three
+  seconds after completing.
+
 ## 0.12.15+11
 
 * Make test iframes visible when debugging.

lib/src/runner/browser/browser_manager.dart

@@ -163,7 +163,7 @@ class BrowserManager {
     _channel = new MultiChannel(webSocket.transform(jsonDocument)
         .changeStream((stream) {
       return stream.map((message) {
-        _timer.reset();
+        if (!_closed) _timer.reset();
         for (var controller in _controllers) {
           controller.setDebugging(false);
         }

pubspec.yaml

@@ -1,5 +1,5 @@
 name: test
-version: 0.12.16-dev
+version: 0.12.15+12
 author: Dart Team <[email protected]>
 description: A library for writing dart unit tests.
 homepage: https://github.com/dart-lang/test