Fix rare browser crash when closing the Origin Info Bubble.

BUG=468201
TEST=Follow the repro steps in the bug and ensure there's no crash.

Review URL: https://codereview.chromium.org/1069043002

Cr-Commit-Position: refs/heads/master@{#324102}

chrome/browser/ui/cocoa/website_settings/website_settings_bubble_controller.mm

@@ -367,6 +367,7 @@ NSColor* IdentityVerifiedTextColor() {
 - (void)windowWillClose:(NSNotification*)notification {
   if (presenter_.get())
     presenter_->OnUIClosing();
+  presenter_.reset();
   [super windowWillClose:notification];
 }