Do not set the mouse event handler if Widget::SetCapture() fails

Do not set the mouse event handler if Widget::SetCapture() fails.
In particular, Widget::SetCapture() fails if the widget is not visible.

BUG=None
TEST=WidgetCaptureTest.FailedCaptureRequestIsNoop

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=283633

[pkotwicz, 2014-07-16 18:50:11]

Scott, can you please take a look? This is a bug I ran into while cleaning up
the Linux mouse capture code

https://codereview.chromium.org/375593002/diff/120001/chrome/browser/ui/views...
File chrome/browser/ui/views/tabs/tab_drag_controller.cc (left):

https://codereview.chromium.org/375593002/diff/120001/chrome/browser/ui/views...
chrome/browser/ui/views/tabs/tab_drag_controller.cc:923: attached_tabstrip_);
This call was added a prior date to
attached_tabstrip_->GetWidget()->SetCapture() being added.

[sky, 2014-07-16 19:39:46]

I'm curious, when does setting capture failure? AFAICT
DesktopWindowTreeHostX11::SetCapture always succeeds.

[pkotwicz, 2014-07-16 19:41:37]

Widget::SetCapture() fails if the widget is not visible

[sky, 2014-07-16 19:41:59]

Ah, makes sense. LGTM

[pkotwicz, 2014-07-16 19:42:31]

The CQ bit was checked by pkotwicz@chromium.org

[pkotwicz, 2014-07-16 19:44:16]

For the sake of completeness, the logic which makes setting capture fail if the
window is not visible is in Window::SetCapture() and is not an X11 curiosity.

[pkotwicz, 2014-07-16 19:45:30]

The CQ bit was unchecked by pkotwicz@chromium.org

[pkotwicz, 2014-07-16 19:46:39]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-07-16 19:48:58]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/375593002/120001

[commit-bot: I haz the power, 2014-07-16 23:03:24]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)

[commit-bot: I haz the power, 2014-07-17 04:04:35]

Change committed as 283633