Fixes crah in NativeWidgetAura::IsActive()

The crash happens if when the HWND is destroyed someone asks if a
child NativeWidgetAura is Active. In particular during this code path
we've gone through ~RootWindow and are in ~Window. When this happens
GetRootWindow() uses Window's implementation, which returns NULL and
we crash.

BUG=264855
TEST=none
R=ben@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23904005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@222096 0039d316-1c4b-4281-b951-d872f2087c98

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) {