Sort out build dependencies for LinuxUI.

Sort out build dependencies for LinuxUI.

LinuxUI now needs to vend NativeTheme instances into code in views/. This means
it can't live in ui/base/ because ui/native_theme depends on ui/base/.

LinuxUI used to live entirely in ui/base/. When ShellDialog was split off of
ui/base/, an intermediary derived interfact was created in ui/shell_dialogs,
requiring casting. This a bit ugly and has been cleaned up.

It makes more sense to have LinuxUI depend on NativeTheme and ShellDialog, and
in turn, be depended on by classes in ui/views/ and chrome/. This patch only moves
files and adds interfaces; the actual NativeThemeGtk2 instance will land in
a separate patch.

BUG=130810
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=185705

[Ben Goodger (Google), 2013-03-01 17:36:11]

I'd stick a note into the new component that it should be folded into views
perhaps once the gtk fe is dead.

LGTM otherwise.

[commit-bot: I haz the power, 2013-03-01 20:35:33]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/erg@chromium.org/12315139/14001

[commit-bot: I haz the power, 2013-03-02 16:08:04]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/erg@chromium.org/12315139/14001

[commit-bot: I haz the power, 2013-03-02 16:45:21]

Change committed as 185705