[Effen] Use the checkbox widget in the stocks app.

[Effen] Use the checkbox widget in the stocks app.

- add a checkbox to the stock app, so that we're testing the checkbox widget
  (it's not currently wired up to anything, that can come later)
- make InkSplash use FlexContainer so that we can use flex in the popup menu items
- make effen's Text be more similar to Image and Container, so that it can be styled
- make layout.dart's RenderCSSText correctly support being styled
- also fixes a bug with the stock list where we were rendering one too few a row when scrolling
- check in the code to dump the DOM so I don't have to keep remembering how to do this

R=eseidel@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/f9e940c3a32cbd4379ad2cc1b3ef1a3f8e8a761e

[eseidel, 2015-05-12 21:34:41]

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

[eseidel, 2015-05-12 21:34:42]

lgtm

https://codereview.chromium.org/1134163003/diff/20001/sky/framework/component...
File sky/framework/components/checkbox.dart (right):

https://codereview.chromium.org/1134163003/diff/20001/sky/framework/component...
sky/framework/components/checkbox.dart:7: import 'dart:sky' as sky;
Do you want this?

[Hixie, 2015-05-12 21:39:46]

Committed patchset #2 (id:20001) manually as
f9e940c3a32cbd4379ad2cc1b3ef1a3f8e8a761e (presubmit successful).