Mac: Fix window ordering for certificate viewer/selector sheets and overlays.

components/constrained_window/native_web_contents_modal_dialog_manager_views_mac.mm

Index: components/constrained_window/native_web_contents_modal_dialog_manager_views_mac.mm
diff --git a/components/constrained_window/native_web_contents_modal_dialog_manager_views_mac.mm b/components/constrained_window/native_web_contents_modal_dialog_manager_views_mac.mm
index 5df747e7ecef4bb8ac1c193e4cdd0835d64b641e..87fb52678d13bc5cc6f8ed5cf7d1f7f1011aafbb 100644
--- a/components/constrained_window/native_web_contents_modal_dialog_manager_views_mac.mm
+++ b/components/constrained_window/native_web_contents_modal_dialog_manager_views_mac.mm
@@ -21,14 +21,19 @@ namespace {
 
 // Sets visibility and mouse events for a Cocoa NSWindow* and an attached sheet.
 void SetSheetVisible(gfx::NativeWindow overlay, bool visible) {
-  CGFloat alpha = visible ? 1.0 : 0.0;
   BOOL ignore_events = visible ? NO : YES;
 
   // Don't allow interaction with the tab underneath the overlay.
   [overlay setIgnoresMouseEvents:ignore_events];
 
-  [[overlay attachedSheet] setAlphaValue:alpha];
+  [[overlay attachedSheet] setAlphaValue:visible ? 1.0 : 0.0];
   [[overlay attachedSheet] setIgnoresMouseEvents:ignore_events];
+
+  // Make sure overlay layers for hidden Cocoa dialogs are always behind
+  // overlays which are in use. If they are not hidden, the attached sheet needs
+  // to be in front of its corresponding overlay window to accept mouse clicks.
+  [overlay setLevel:visible ? 1 : 0];
+  [[overlay attachedSheet] setLevel:visible ? 2 : 0];
 }
 
 }  // namespace