Avoid blocking while mapping an X11 window

ui/events/platform/x11/x11_event_source.h

 // Copyright 2014 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.
 
 #ifndef UI_EVENTS_PLATFORM_X11_X11_EVENT_SOURCE_H_
 #define UI_EVENTS_PLATFORM_X11_X11_EVENT_SOURCE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 47 matching lines @@
 
   // Blocks on the X11 event queue until we receive notification from the
   // xserver that |w| has been mapped; StructureNotifyMask events on |w| are
   // pulled out from the queue and dispatched out of order.
   //
   // For those that know X11, this is really a wrapper around XWindowEvent
   // which still makes sure the preempted event is dispatched instead of
   // dropped on the floor. This method exists because mapping a window is
   // asynchronous (and we receive an XEvent when mapped), while there are also
   // functions which require a mapped window.
   void BlockUntilWindowMapped(XID window);

[Tom (Use chromium acct), 2016/09/26 17:26:04]

This should be done in the future, but I just want to document it here for now. 
There are only 2 remaining places that calls BlockUntilWindowMapped, and those
are in x11_window_base.cc and x11_whole_screen_move_loop.cc.  The former is just
like this case, and should be removed.  The other is done on an
override-redirect window, so we don't need to block for a map.

This means we can remove BlockUntilWindowMapped and BlockOnWindowStructureEvent.

 
-  void BlockUntilWindowUnmapped(XID window);
-
   XDisplay* display() { return display_; }
 
   // Returns the timestamp of the event currently being dispatched.  Falls back
   // on GetCurrentServerTime() if there's no event being dispatched, or if the
   // current event does not have a timestamp.
   Time GetTimestamp();
 
   void StopCurrentEventStream();
   void OnDispatcherListChanged();
 
@@ skipping 35 matching lines @@
   bool continue_stream_ = true;
 
   std::unique_ptr<X11HotplugEventHandler> hotplug_event_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(X11EventSource);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_PLATFORM_X11_X11_EVENT_SOURCE_H_