Rationalise hit testing in the new RenderNode world

Rationalise hit testing in the new RenderNode world

- makes the event logic not involve a boolean return value (since we ignored it anyway)
- splits the event handling logic into two steps, hit testing and event dispatch
- introduces an App class on the Dart side to factor out the interaction with the C++ side
- ports sector-layout and simple_render_tree to the new App infrastructure
- port simple_render_tree to the new event handling logic
- implement hit testing for the sector-layout demo

R=eseidel@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/a865f73d9c1044e223776c0c8c4abf6be11b5e48

[eseidel, 2015-05-26 19:38:22]

eseidel@chromium.org changed reviewers:
+ eseidel@chromium.org

[eseidel, 2015-05-26 19:38:23]

lgtm

https://codereview.chromium.org/1143343004/diff/1/sky/sdk/lib/framework/layou...
File sky/sdk/lib/framework/layout2.dart (right):

https://codereview.chromium.org/1143343004/diff/1/sky/sdk/lib/framework/layou...
sky/sdk/lib/framework/layout2.dart:495: if (x < 0.0 || x >= width || y < 0.0 ||
y >= height)
If we had a Rect class it could abstract this away.  rect.contains(point).

[Hixie, 2015-05-26 19:44:39]

Committed patchset #1 (id:1) manually as
a865f73d9c1044e223776c0c8c4abf6be11b5e48 (presubmit successful).

[Hixie, 2015-05-26 19:44:52]

> sky/sdk/lib/framework/layout2.dart:495: if (x < 0.0 || x >= width || y < 0.0
|| y >= height)
> If we had a Rect class it could abstract this away.  rect.contains(point).

https://github.com/domokit/mojo/issues/177