Fixes crah in NativeWidgetAura::IsActive()

ui/views/widget/native_widget_aura.cc

Index: ui/views/widget/native_widget_aura.cc
diff --git a/ui/views/widget/native_widget_aura.cc b/ui/views/widget/native_widget_aura.cc
index f9ebed7e85f388a420e328720d7936ed7b80cc52..86012a5b5c49a84a21366e22678f38dd30a5b3ea 100644
--- a/ui/views/widget/native_widget_aura.cc
+++ b/ui/views/widget/native_widget_aura.cc
@@ -521,9 +521,14 @@ void NativeWidgetAura::Deactivate() {
 }
 
 bool NativeWidgetAura::IsActive() const {
-  return window_ &&
-      aura::client::GetActivationClient(window_->GetRootWindow())->
-          GetActiveWindow() == window_;
+  if (!window_)
+    return false;
+
+  // We may up here during destruction of the root, in which case
+  // GetRootWindow() returns NULL (~RootWindow() has run and we're in ~Window).
+  aura::RootWindow* root = window_->GetRootWindow();
+  return root &&
+      aura::client::GetActivationClient(root)->GetActiveWindow() == window_;
 }
 
 void NativeWidgetAura::SetAlwaysOnTop(bool on_top) {