Redesigns the text input focus handling.

ui/views/widget/desktop_aura/x11_desktop_handler.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/widget/desktop_aura/x11_desktop_handler.h"
 
 #include <X11/Xatom.h>
 #include <X11/Xlib.h>
 
 #include "base/message_loop/message_loop.h"
@@ skipping 171 matching lines @@
 }
 
 void X11DesktopHandler::OnActiveWindowChanged(::Window xid) {
   if (current_window_ == xid)
     return;
   DesktopWindowTreeHostX11* old_host =
       views::DesktopWindowTreeHostX11::GetHostForXID(current_window_);
   if (old_host)
     old_host->HandleNativeWidgetActivationChanged(false);
 
+  // Update the current window ID to effectively change the active widget.
+  current_window_ = xid;

[msw, 2014/04/18 19:57:57]

Can you explain why this change is needed for this CL? (just reply here and
perhaps explain in the CL description, which is woefully lacking in details).

[Yuki, 2014/04/22 09:09:02]

It's because we have to change the active widget before calling a callback
function HandleNativeWidgetActivationChanged(), so in that callback function,
|new_host|'s widget has already got activated.

Note that, in this CL, the active widget has an important role.  We allow the
active widget's focus manager to control the text input focus.  So it's
important if the widget is active or not.

Updated the description.

+
   DesktopWindowTreeHostX11* new_host =
       views::DesktopWindowTreeHostX11::GetHostForXID(xid);
   if (new_host)
     new_host->HandleNativeWidgetActivationChanged(true);
-
-  current_window_ = xid;
 }
 
 }  // namespace views