[UI Views] Unset the extension keybinding registry on frame destruction

Some destruction flows don't seem to call OnWidgetActivationChanged
before destroying the window, which causes the extension keybinding
registry reference in the global registry to become stale. Update the
active registry on deletion.

BUG=616970

Review-Url: https://codereview.chromium.org/2046653002
Cr-Commit-Position: refs/heads/master@{#398167}

chrome/browser/ui/views/frame/browser_view.cc

@@ -479,6 +479,12 @@ BrowserView::~BrowserView() {
   }
 #endif
 
+  extensions::ExtensionCommandsGlobalRegistry* global_registry =
+      extensions::ExtensionCommandsGlobalRegistry::Get(browser_->profile());
+  if (global_registry->registry_for_active_window() ==
+          extension_keybinding_registry_.get())
+    global_registry->set_registry_for_active_window(nullptr);
+
   // We destroy the download shelf before |browser_| to remove its child
   // download views from the set of download observers (since the observed
   // downloads can be destroyed along with |browser_| and the observer