Revert "Make Zone API strong mode clean."

tests/lib_strong/async/zone_fork_test.dart

Index: tests/lib_strong/async/zone_fork_test.dart
diff --git a/tests/lib_strong/async/zone_fork_test.dart b/tests/lib_strong/async/zone_fork_test.dart
index 7afbfdea1d43932e8302c811e0fa87f8c694630e..f3d98ea68a942ce76bbf6fb4a93f5e57f0185ab1 100644
--- a/tests/lib_strong/async/zone_fork_test.dart
+++ b/tests/lib_strong/async/zone_fork_test.dart
@@ -19,9 +19,9 @@ main() {
     // is the root zone. (The origin zone hasn't been set yet).
     Expect.identical(Zone.ROOT, Zone.current);
     events.add("forked.fork");
-    var descriptionRun = zoneSpecification.run;
+    Function descriptionRun = zoneSpecification.run;
     ZoneSpecification modified = new ZoneSpecification.from(zoneSpecification,
-        run: <R>(self, parent, origin, R f()) {
+        run: (self, parent, origin, f) {
       events.add("wrapped run");
       return descriptionRun(self, parent, origin, () {
         events.add("wrapped f");
@@ -33,7 +33,7 @@ main() {
 
   events.add("start");
   Zone forkedChild = forked.fork(specification: new ZoneSpecification(
-      run: <R>(Zone self, ZoneDelegate parent, Zone origin, R f()) {
+      run: (Zone self, ZoneDelegate parent, Zone origin, f()) {
     events.add("executing child run");
     return parent.run(origin, f);
   }));