Make browser tests all run from a server instead of the local filesystem.

tests/co19/test_config.dart

Index: tests/co19/test_config.dart
diff --git a/tests/co19/test_config.dart b/tests/co19/test_config.dart
index dc0c92fc1584712cebb582a92942508fca72d204..d3035ff0d39bfb55ccd625e059b05accffa578b8 100644
--- a/tests/co19/test_config.dart
+++ b/tests/co19/test_config.dart
@@ -17,7 +17,8 @@ class Co19TestSuite extends StandardTestSuite {
               ["tests/co19/co19-compiler.status",
                "tests/co19/co19-runtime.status",
                "tests/co19/co19-dart2dart.status",
-               "tests/co19/co19-dart2js.status"]);
+               "tests/co19/co19-dart2js.status"],
+              []);
 
   bool isTestFile(String filename) => _testRegExp.hasMatch(filename);
   bool get listRecursively => true;