Handle WebContentsViewMac being destroyed while a <select> menu is showing.

content/browser/browser_plugin/browser_plugin_popup_menu_helper_mac.h

Index: content/browser/browser_plugin/browser_plugin_popup_menu_helper_mac.h
diff --git a/content/browser/browser_plugin/browser_plugin_popup_menu_helper_mac.h b/content/browser/browser_plugin/browser_plugin_popup_menu_helper_mac.h
index 7dc9b6582a2c7bb52067e34a76a4edf97022764e..ebb46abce681444f7328a41a5a0c480eff8d4688 100644
--- a/content/browser/browser_plugin/browser_plugin_popup_menu_helper_mac.h
+++ b/content/browser/browser_plugin/browser_plugin_popup_menu_helper_mac.h
@@ -15,7 +15,8 @@ class RenderFrameHostImpl;
 
 // This class is similiar to PopupMenuHelperMac but positions the popup relative
 // to the embedder, and issues a reply to the guest.
-class BrowserPluginPopupMenuHelper : public PopupMenuHelper {
+class BrowserPluginPopupMenuHelper : public PopupMenuHelper,
+                                     public PopupMenuHelper::Delegate {
  public:
   // Creates a BrowserPluginPopupMenuHelper that positions popups relative to
   // |embedder_rfh| and will notify |guest_rfh| when a user selects or cancels
@@ -24,8 +25,12 @@ class BrowserPluginPopupMenuHelper : public PopupMenuHelper {
                                RenderFrameHost* guest_rfh);
 
  private:
+  // PopupMenuHelper:
   RenderWidgetHostViewMac* GetRenderWidgetHostView() const override;
 
+  // PopupMenuHelper:Delegate:
+  void OnMenuClosed() override;
+
   RenderFrameHostImpl* embedder_rfh_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserPluginPopupMenuHelper);