Rename unsubscribe to cancel.

sdk/lib/io/file_impl.dart

Index: sdk/lib/io/file_impl.dart
diff --git a/sdk/lib/io/file_impl.dart b/sdk/lib/io/file_impl.dart
index 761a794400c0436e31119c5a7bc4bed435cae339..c5d77ec4f9df2875264e5258671c3596f5e82628 100644
--- a/sdk/lib/io/file_impl.dart
+++ b/sdk/lib/io/file_impl.dart
@@ -576,12 +576,12 @@ class _File extends _FileBase implements File {
     return open(mode).then((file) {
       var controller = new StreamController();
 
-      var subscription = controller.subscribe();
-      subscription.onData((data) {
-        // TODO(ajohnsen): handle errors correctly.
-        file.writeList(data, 0, data.length);
-      });
-      subscription.onDone(file.close);
+      var subscription = controller.listen(
+        (data) {
+          // TODO(ajohnsen): handle errors correctly.
+          file.writeList(data, 0, data.length);
+        },
+        onDone: file.close);
 
       return controller.sink;
     });