Use generic functions in zones.

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 0a32721152a041d7025b4a00f8da1369259a5b8b..198f9e3eeff75e0c51e6b39ccccca084d0a750fd 100644
--- a/tools/testing/dart/test_runner.dart
+++ b/tools/testing/dart/test_runner.dart
@@ -1012,8 +1012,9 @@ class CommandQueue {
       // If a command is part of many TestCases we set the timeout to be
       // the maximum over all [TestCase.timeout]s. At some point, we might
       // eliminate [TestCase.timeout] completely and move it to [Command].
-      int timeout =
-          testCases.map((TestCase test) => test.timeout).fold(0, math.max);
+      int timeout = testCases
+          .map((TestCase test) => test.timeout)
+          .fold(0, (int a, b) => math.max(a, b));
 
       if (_verbose) {
         print('Running "${command.displayName}" command: $command');