MacViews: Support ui::MODAL_TYPE_WINDOW with a null parent window.

ui/views/widget/native_widget_mac.mm

 // 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.
 
 #include "ui/views/widget/native_widget_mac.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include <utility>
 
@@ skipping 78 matching lines @@
   id<NSWindowDelegate> window_delegate = [window delegate];
   if ([window_delegate respondsToSelector:@selector(nativeWidgetMac)]) {
     ViewsNSWindowDelegate* delegate =
         base::mac::ObjCCastStrict<ViewsNSWindowDelegate>(window_delegate);
     return [delegate nativeWidgetMac]->bridge_.get();
   }
   return nullptr;  // Not created by NativeWidgetMac.
 }
 
 bool NativeWidgetMac::IsWindowModalSheet() const {
-  return GetWidget()->widget_delegate()->GetModalType() ==
-         ui::MODAL_TYPE_WINDOW;
+  return bridge_ && bridge_->parent() &&
+         GetWidget()->widget_delegate()->GetModalType() ==
+             ui::MODAL_TYPE_WINDOW;
 }
 
 void NativeWidgetMac::OnWindowWillClose() {
   // Note: If closed via CloseNow(), |bridge_| will already be reset. If closed
   // by the user, or via Close() and a RunLoop, notify observers while |bridge_|
   // is still a valid pointer, then reset it.
   if (bridge_) {
     delegate_->OnNativeWidgetDestroying();
     [GetNativeWindow() setDelegate:nil];
     bridge_.reset();
@@ skipping 174 matching lines @@
                                      const gfx::ImageSkia& app_icon) {
   NOTIMPLEMENTED();
 }
 
 void NativeWidgetMac::InitModalType(ui::ModalType modal_type) {
   if (modal_type == ui::MODAL_TYPE_NONE)
     return;
 
   // System modal windows not implemented (or used) on Mac.
   DCHECK_NE(ui::MODAL_TYPE_SYSTEM, modal_type);
-  DCHECK(bridge_->parent());
-  // Everyhing happens upon show.
+
+  // A peculiarity of the constrained window framework is that it permits a
+  // dialog of MODAL_TYPE_WINDOW to have a null parent window; falling back to
+  // a non-modal window in this case.
+  DCHECK(bridge_->parent() || modal_type == ui::MODAL_TYPE_WINDOW);
+
+  // Everything happens upon show.
 }
 
 gfx::Rect NativeWidgetMac::GetWindowBoundsInScreen() const {
   return gfx::ScreenRectFromNSRect([GetNativeWindow() frame]);
 }
 
 gfx::Rect NativeWidgetMac::GetClientAreaBoundsInScreen() const {
   NSWindow* window = GetNativeWindow();
   return gfx::ScreenRectFromNSRect(
       [window contentRectForFrameRect:[window frame]]);
@@ skipping 452 matching lines @@
   [[ViewsNSWindowCloseAnimator alloc] initWithWindow:window];
 }
 
 - (void)animationDidEnd:(NSAnimation*)animation {
   [window_ close];
   [animation_ setDelegate:nil];
   [self release];
 }
 
 @end