Fixed (currently harmless) bug in test_runner and implemented separate dart2js compilation cache

tools/testing/dart/test_runner.dart

Index: tools/testing/dart/test_runner.dart
diff --git a/tools/testing/dart/test_runner.dart b/tools/testing/dart/test_runner.dart
index 8e1363af458b18cbacf6c02dc3e0b04bd0c7093b..a396abdd4d27832a1f19ac159a413cd97b3a103d 100644
--- a/tools/testing/dart/test_runner.dart
+++ b/tools/testing/dart/test_runner.dart
@@ -2155,6 +2155,10 @@ class TestCaseCompleter {
     // (i.e. before state changes in the graph)
     commandQueue.completedCommands.listen((CommandOutput output) {
       _outputs[output.command] = output;
+    }, onDone: () {
+      _completeTestCasesIfPossible(new List.from(enqueuer.remainingTestCases));
+      assert(enqueuer.remainingTestCases.isEmpty);
+      _checkDone();
     });
 
     // Listen for NodeState.Processing -> NodeState.{Successfull,Failed}
@@ -2162,15 +2166,13 @@ class TestCaseCompleter {
     eventCondition((event) => event is dgraph.StateChangedEvent)
         .listen((dgraph.StateChangedEvent event) {
           if (event.from == dgraph.NodeState.Processing) {
+            var command = event.node.userData;
+
             assert(COMPLETED_STATES.contains(event.to));
-            _completeTestCasesIfPossible(event.node.userData);
+            assert(_outputs[command] != null);
 
-            if (!_closed &&
-                graph.isSealed &&
-                enqueuer.remainingTestCases.isEmpty) {
-              _controller.close();
-              _closed = true;
-            }
+            _completeTestCasesIfPossible(enqueuer.command2testCases[command]);
+            _checkDone();
           }
     });
 
@@ -2187,11 +2189,14 @@ class TestCaseCompleter {
 
   Stream<TestCase> get finishedTestCases => _controller.stream;
 
-  void _completeTestCasesIfPossible(Command command) {
-    assert(_outputs[command] != null);
-
-    var testCases = enqueuer.command2testCases[command];
+  void _checkDone() {
+    if (!_closed && graph.isSealed && enqueuer.remainingTestCases.isEmpty) {
+      _controller.close();
+      _closed = true;
+    }
+  }
 
+  void _completeTestCasesIfPossible(Iterable<TestCase> testCases){
     // Update TestCases with command outputs
     for (TestCase test in testCases) {
       for (var icommand in test.commands) {