Speculative fix for instant overlay crash

chrome/browser/ui/cocoa/tab_contents/instant_overlay_controller_mac.mm

Index: chrome/browser/ui/cocoa/tab_contents/instant_overlay_controller_mac.mm
diff --git a/chrome/browser/ui/cocoa/tab_contents/instant_overlay_controller_mac.mm b/chrome/browser/ui/cocoa/tab_contents/instant_overlay_controller_mac.mm
index 34b6a824b49d915446ff7759bb823ecc2a858301..b5c04ceeef0a577952a4667a988da394b6203f0b 100644
--- a/chrome/browser/ui/cocoa/tab_contents/instant_overlay_controller_mac.mm
+++ b/chrome/browser/ui/cocoa/tab_contents/instant_overlay_controller_mac.mm
@@ -13,6 +13,8 @@
 #include "chrome/browser/ui/search/search_model.h"
 #include "chrome/browser/ui/search/search_tab_helper.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
+#include "content/public/browser/notification_source.h"
+#include "content/public/browser/notification_types.h"
 
 InstantOverlayControllerMac::InstantOverlayControllerMac(
     Browser* browser,
@@ -69,4 +71,20 @@ void InstantOverlayControllerMac::OverlayStateChanged(
   }
 
   [window_ updateBookmarkBarStateForInstantOverlay];
+
+  registrar_.RemoveAll();
+  if (model.GetOverlayContents()) {
+    registrar_.Add(
+        this,
+        content::NOTIFICATION_WEB_CONTENTS_DESTROYED,
+        content::Source<content::WebContents>(model.GetOverlayContents()));
+  }
+}
+
+void InstantOverlayControllerMac::Observe(
+    int type,
+    const content::NotificationSource& source,
+    const content::NotificationDetails& details) {
+  [overlay_ onWebContentsDestroyed:
+          content::Source<content::WebContents>(source).ptr()];
 }