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..aafe789f935296b8f395fa6d4ad68b26bfcb5ba4 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 +21,25 @@ 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];
+
+  if (visible) {
+    // When showing the sheet, re-order the overlay and sheet to be on top of
+    // any other sheet/overlay pairs which may be open at the same time. Without
+    // doing this, the sheet and overlay become obscured behind overlays for
+    // other sheets, which block mouse events intended for the current sheet.
+    NSWindow* parent = [overlay parentWindow];
+    [parent removeChildWindow:overlay];
+    [parent addChildWindow:overlay ordered:NSWindowAbove];
+    [overlay removeChildWindow:[overlay attachedSheet]];
+    [overlay addChildWindow:[overlay attachedSheet] ordered:NSWindowAbove];
+  }
 }
 
 }  // namespace