Emit OnNativeWidgetDestroying() before clearing the NSWindowDelegate.

ui/views/cocoa/bridged_native_widget.mm

Index: ui/views/cocoa/bridged_native_widget.mm
diff --git a/ui/views/cocoa/bridged_native_widget.mm b/ui/views/cocoa/bridged_native_widget.mm
index b0ab01429cdce334feb89a25766c3dd61b38532a..f2ed000a4b5cec36f6f3552a06262888752be29c 100644
--- a/ui/views/cocoa/bridged_native_widget.mm
+++ b/ui/views/cocoa/bridged_native_widget.mm
@@ -342,39 +342,23 @@ NSComparisonResult SubviewSorter(NSViewComparatorValue lhs,
 }
 
 BridgedNativeWidget::~BridgedNativeWidget() {
-  bool close_window = false;
-  if ([window_ delegate]) {
-    // If the delegate is still set on a modal dialog, it means it was not
-    // closed via [NSApplication endSheet:]. This is probably OK if the widget
-    // was never shown. But Cocoa ignores close() calls on open sheets. Calling
-    // endSheet: here would work, but it messes up assumptions elsewhere. E.g.
-    // DialogClientView assumes its delegate is alive when closing, which isn't
-    // true after endSheet: synchronously calls OnNativeWidgetDestroyed().
-    // So ban it. Modal dialogs should be closed via Widget::Close().
-    DCHECK(!native_widget_mac_->IsWindowModalSheet());
-
-    // If the delegate is still set, it means OnWindowWillClose() has not been
-    // called and the window is still open. Usually, -[NSWindow close] would
-    // synchronously call OnWindowWillClose() which removes the delegate and
-    // notifies NativeWidgetMac, which then calls this with a nil delegate.
-    // For other teardown flows (e.g. Widget::WIDGET_OWNS_NATIVE_WIDGET or
-    // Widget::CloseNow()) the delegate must first be cleared to avoid AppKit
-    // calling back into the bridge. This means OnWindowWillClose() needs to be
-    // invoked manually, which is done below.
-    // Note that if the window has children it can't be closed until the
-    // children are gone, but removing child windows calls into AppKit for the
-    // parent window, so the delegate must be cleared first.
-    [window_ setDelegate:nil];
-    close_window = true;
-  }
+  // If the delegate is still set on a modal dialog, it means it was not
+  // closed via [NSApplication endSheet:]. This is probably OK if the widget
+  // was never shown. But Cocoa ignores close() calls on open sheets. Calling
+  // endSheet: here would work, but it messes up assumptions elsewhere. E.g.
+  // DialogClientView assumes its delegate is alive when closing, which isn't
+  // true after endSheet: synchronously calls OnNativeWidgetDestroyed().
+  // So ban it. Modal dialogs should be closed via Widget::Close().
+  DCHECK(!close_window_ || !native_widget_mac_->IsWindowModalSheet());
 
+  [window_ setDelegate:nil];
   RemoveOrDestroyChildren();
   DCHECK(child_windows_.empty());
   SetFocusManager(nullptr);
   SetRootView(nullptr);
   DestroyCompositor();
 
-  if (close_window) {
+  if (close_window_) {
     OnWindowWillClose();
     [window_ close];
   }
@@ -707,7 +691,7 @@ NSComparisonResult SubviewSorter(NSViewComparatorValue lhs,
     parent_->RemoveChildWindow(this);
     parent_ = nullptr;
   }
-  [window_ setDelegate:nil];
+  close_window_ = false;
   [[NSNotificationCenter defaultCenter] removeObserver:window_delegate_];
   native_widget_mac_->OnWindowWillClose();

[tapted, 2016/10/05 08:38:18]

Is the problem just that NativeWidgetMac::OnWindowWillClose() invokes
OnWindowDestroying() too late?

What about making this method something like

void BridgedNativeWidget::OnWindowWillClose() {
  native_widget_mac_->OnWindowDestroying();
  /* everything else */
  native_widget_mac_->OnWindowDestroyed();
}

(i.e. split NativeWidgetMac::OnWindowWillClose into two methods -- this will
move the implementation closer to what NativeWidgetAura is already doing).

 }