Refactor Navigator to put state in separate class, initial back button plumbing

Refactor Navigator to put state in separate class, initial back button plumbing

R=abarth@chromium.org, abarth

Committed: https://chromium.googlesource.com/external/mojo/+/e3ee7195a7314edd369d89f671a3ab18823fe4a0

[abarth-chromium, 2015-06-17 18:55:20]

lgtm

https://codereview.chromium.org/1195493002/diff/1/sky/sdk/lib/app/view.dart
File sky/sdk/lib/app/view.dart (right):

https://codereview.chromium.org/1195493002/diff/1/sky/sdk/lib/app/view.dart#n...
sky/sdk/lib/app/view.dart:18: typedef void EventListener(sky.Event event);
You should already have this type as sky.EventListener

[jackson, 2015-06-17 19:21:15]

Committed patchset #2 (id:20001) manually as
e3ee7195a7314edd369d89f671a3ab18823fe4a0 (presubmit successful).

[Hixie, 2015-06-17 19:29:42]

ianh@google.com changed reviewers:
+ ianh@google.com

[Hixie, 2015-06-17 19:29:43]

lgtm

https://codereview.chromium.org/1195493002/diff/20001/sky/sdk/lib/app/view.dart
File sky/sdk/lib/app/view.dart (right):

https://codereview.chromium.org/1195493002/diff/20001/sky/sdk/lib/app/view.da...
sky/sdk/lib/app/view.dart:53: List<sky.EventListener> eventListeners = new
List<sky.EventListener>();
Make this final, at least.

But ideally, we'd have an interface here where you can add (and remove)
listeners. Otherwise, random people can clear the list, send events to random
callbacks, etc.

Also, we shouldn't use sky.EventListener. Just use a typedef for a callback.

https://codereview.chromium.org/1195493002/diff/20001/sky/sdk/lib/widgets/wid...
File sky/sdk/lib/widgets/widget.dart (right):

https://codereview.chromium.org/1195493002/diff/20001/sky/sdk/lib/widgets/wid...
sky/sdk/lib/widgets/widget.dart:802:
WidgetAppView._appView.eventListeners.add((event) {
This shouldn't use the underbar version. If there's no way to get to the appview
from here without using privates, then we have a bigger problem.