Make DesktopWindowTreeHostX11::use_native_frame_ more robust

Make |DesktopWindowTreeHostX11::use_native_frame_| more robust. In particular, this CL ensures that widgets which expect to use the native frame (e.g. v2 apps, task manager) continue to do so even if DesktopWindowTreeHostX11::FrameTypeChanged() is called.

BUG=348437
TEST=None

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=271986

[pkotwicz, 2014-05-13 00:11:53]

erg@ PTAL

I realize that things would not work if a caller called
Widget::set_frame_type(Widget::FRAME_TYPE_FORCE_CUSTOM);
Widget::set_frame_type(Widget::FRAME_TYPE_DEFAULT);
in sequence.

[Elliot Glaysher, 2014-05-13 00:19:03]

lgtm

[pkotwicz, 2014-05-20 17:15:42]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-05-20 17:17:57]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/278823004/40001

[commit-bot: I haz the power, 2014-05-20 21:24:05]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  android_dbg_triggered_tests on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_dbg_triggered...)

[commit-bot: I haz the power, 2014-05-20 22:29:53]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-05-20 22:29:53]

Try jobs failed on following builders:
  android_dbg_triggered_tests on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_dbg_triggered...)

[pkotwicz, 2014-05-21 00:08:47]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-05-21 00:09:59]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/278823004/40001

[commit-bot: I haz the power, 2014-05-21 20:02:10]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  android_dbg_triggered_tests on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_dbg_triggered...)

[commit-bot: I haz the power, 2014-05-21 22:25:15]

Change committed as 271986