Add GetDefaultIndex() to ComboboxModel.

Add GetDefaultIndex() to ComboboxModel.

BUG=none

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=184532

[sky, 2013-02-22 05:57:40]

LGTM

[commit-bot: I haz the power, 2013-02-22 21:08:59]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/estade@chromium.org/12335026/10002

[commit-bot: I haz the power, 2013-02-22 22:04:10]

Sorry for I got bad news for ya.
Compile failed with a clobber build on linux_rel.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...
Your code is likely broken or HEAD is junk. Please ensure your
code is not broken then alert the build sheriffs.
Look at the try server FAQ for more details.

[commit-bot: I haz the power, 2013-02-22 22:07:54]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/estade@chromium.org/12335026/14003

[commit-bot: I haz the power, 2013-02-22 22:36:25]

Sorry for I got bad news for ya.
Compile failed with a clobber build on linux_clang.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_clan...
Your code is likely broken or HEAD is junk. Please ensure your
code is not broken then alert the build sheriffs.
Look at the try server FAQ for more details.

[Evan Stade, 2013-02-25 23:54:19]

Scott, do you have any idea why this is failing on clang trybots? It works
locally with clang, and passes on non-clang trybots, but for some reason clang
trybots don't seem to be able to link against the function in combobox_model.cc.

[tfarina, 2013-02-26 00:00:03]

I think the following should fix it. It wasn't necessary because everything was
in the header/inlined.

https://codereview.chromium.org/12335026/diff/6008/ui/base/models/combobox_mo...
File ui/base/models/combobox_model.h (right):

https://codereview.chromium.org/12335026/diff/6008/ui/base/models/combobox_mo...
ui/base/models/combobox_model.h:14: class ComboboxModel {
class UI_EXPORT ?

[Evan Stade, 2013-02-26 00:03:44]

thank you, I feel dumb. I figured out I needed the ui_export.h include but
somehow missed actually using.

[Evan Stade, 2013-02-26 00:51:53]

Committed patchset #8 manually as r184532 (presubmit successful).