Properly set the exit code for failing tests run directly.

test/runner/runner_test.dart

Index: test/runner/runner_test.dart
diff --git a/test/runner/runner_test.dart b/test/runner/runner_test.dart
index 5e038127650cbbd3f78813e7e8c3063de60b3c0f..963feaf3fa223b1bbf3c21c14e6358baf7cb32d6 100644
--- a/test/runner/runner_test.dart
+++ b/test/runner/runner_test.dart
@@ -285,6 +285,7 @@ $_usage"""));
         "test.dart"
       ]);
       expect(result.stdout, contains("All tests passed!"));
+      expect(result.exitCode, equals(0));
     });
 
     // Regression test; this broke in 0.12.0-beta.9.
@@ -332,6 +333,7 @@ $_usage"""));
         "test.dart"
       ]);
       expect(result.stdout, contains("Some tests failed."));
+      expect(result.exitCode, isNot(equals(0)));
     });
   });