mash shelf: Don't create shelf DimmerView in ShelfWidget on mus

mash shelf: Don't create shelf DimmerView in ShelfWidget on mus

This removes another aura dependency from ShelfWidget.

* Introduce a pure-virtual interface for the DimmerView.
* Delegate creation of the WmDimmerView out via WmShelf.
* Return a null WmDimmerView on mus, indicating dimming is not supported.
* Clean up some |shelf| vs. |shelf_widget| confusion in ShelfWidget.

BUG=615155
TEST=existing ash_unittests

Committed: https://crrev.com/896df1b1c68d4463c8ff5f05ff2c8b60a7d2e52b
Cr-Commit-Position: refs/heads/master@{#410896}

[James Cook, 2016-08-09 23:40:01]

The CQ bit was checked by jamescook@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-08-09 23:40:43]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[James Cook, 2016-08-09 23:41:27]

jamescook@chromium.org changed reviewers:
+ msw@chromium.org

[James Cook, 2016-08-09 23:41:28]

msw, please take a look.

I went the pure-virtual interface route as it ended up being cleaner than
throwing methods on WmShelf. I'm not thrilled with the name WmDimmerView,
especially since it isn't a concrete base class of DimmerView, but I wanted to
tie it to DimmerView and couldn't think of something better.

[msw, 2016-08-09 23:48:58]

lgtm

[James Cook, 2016-08-09 23:55:20]

The CQ bit was unchecked by jamescook@chromium.org

[James Cook, 2016-08-09 23:55:26]

The CQ bit was checked by jamescook@chromium.org

[commit-bot: I haz the power, 2016-08-09 23:56:37]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-10 00:30:49]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-08-10 00:32:56]

Description was changed from

==========
mash shelf: Don't create shelf DimmerView in ShelfWidget on mus

This removes another aura dependency from ShelfWidget.

* Introduce a pure-virtual interface for the DimmerView.
* Delegate creation of the WmDimmerView out via WmShelf.
* Return a null WmDimmerView on mus, indicating dimming is not supported.
* Clean up some |shelf| vs. |shelf_widget| confusion in ShelfWidget.

BUG=615155
TEST=existing ash_unittests
==========

to

==========
mash shelf: Don't create shelf DimmerView in ShelfWidget on mus

This removes another aura dependency from ShelfWidget.

* Introduce a pure-virtual interface for the DimmerView.
* Delegate creation of the WmDimmerView out via WmShelf.
* Return a null WmDimmerView on mus, indicating dimming is not supported.
* Clean up some |shelf| vs. |shelf_widget| confusion in ShelfWidget.

BUG=615155
TEST=existing ash_unittests

Committed: https://crrev.com/896df1b1c68d4463c8ff5f05ff2c8b60a7d2e52b
Cr-Commit-Position: refs/heads/master@{#410896}
==========

[commit-bot: I haz the power, 2016-08-10 00:32:57]

Patchset 2 (id:??) landed as
https://crrev.com/896df1b1c68d4463c8ff5f05ff2c8b60a7d2e52b
Cr-Commit-Position: refs/heads/master@{#410896}