[Views] Make MenuButton track its desired state while pressed

ui/views/widget/desktop_aura/desktop_native_widget_aura.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/desktop_native_widget_aura.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/cursor_client.h"
@@ skipping 852 matching lines @@
 
 void DesktopNativeWidgetAura::SetCursor(gfx::NativeCursor cursor) {
   cursor_ = cursor;
   aura::client::CursorClient* cursor_client =
       aura::client::GetCursorClient(host_->window());
   if (cursor_client)
     cursor_client->SetCursor(cursor);
 }
 
 bool DesktopNativeWidgetAura::IsMouseEventsEnabled() const {
-  if (!content_window_)
+  if (!content_window_ || !host_)

[sky, 2015/01/24 00:00:36]

This has me worried, and at the least is worth a comment. Why do we need to
check for no host here when no where else in this class do we do it?

[Devlin, 2015/01/24 00:11:48]

Yeah, I'm not real keen on it either.
Reason:
- OnHostClosed() resets() |host_|, and then sets |content_window_| to null.
- |host_|'s destructor works its way around to calling OnWidgetDestroying.
- OnWidgetDestroying is a path for release MenuButton::PressedLocks.
- Releasing the last pressed lock checks if the mouse is hovered, which checks
if IsMouseEventsEnabled() (leads to crash).

In short, checking if mouse events are enabled during a widget shutdown crashes.
 I was wondering about other possible solutions (mark a widget as destroying in
views::Widget, and don't check it if it is? [Seems like a bandaid, not a
solution.]  Set content_window_ to null before resetting host_? [Tried that one;
it fails because destruction/reset order is hyper-sensitive]).

This seemed like the safest solution, because it's common to check something for
nullness before using it (on line 876), but I'd love your opinion.

     return false;
   aura::client::CursorClient* cursor_client =
       aura::client::GetCursorClient(host_->window());
   return cursor_client ? cursor_client->IsMouseEventsEnabled() : true;
 }
 
 void DesktopNativeWidgetAura::ClearNativeFocus() {
   desktop_window_tree_host_->ClearNativeFocus();
 
   if (ShouldActivate()) {
@@ skipping 345 matching lines @@
   if (cursor_reference_count_ == 0) {
     // We are the last DesktopNativeWidgetAura instance, and we are responsible
     // for cleaning up |cursor_manager_|.
     delete cursor_manager_;
     native_cursor_manager_ = NULL;
     cursor_manager_ = NULL;
   }
 }
 
 }  // namespace views