Hook up proper FocusController for simple_wm.

ui/views/window/custom_frame_view.h

Index: ui/views/window/custom_frame_view.h
diff --git a/ui/views/window/custom_frame_view.h b/ui/views/window/custom_frame_view.h
index 8869bef4aa3fca5afbbcd1372d19fdff6ffae78a..76d4fc26bc6d5445d90d763d6cff203694afb3ae 100644
--- a/ui/views/window/custom_frame_view.h
+++ b/ui/views/window/custom_frame_view.h
@@ -46,6 +46,7 @@ class VIEWS_EXPORT CustomFrameView : public NonClientFrameView,
   void UpdateWindowIcon() override;
   void UpdateWindowTitle() override;
   void SizeConstraintsChanged() override;
+  void ActivationChanged(bool active) override;
 
   // Overridden from View:
   void OnPaint(gfx::Canvas* canvas) override;
@@ -152,6 +153,10 @@ class VIEWS_EXPORT CustomFrameView : public NonClientFrameView,
   int minimum_title_bar_x_;
   int maximum_title_bar_x_;
 
+  // True if the frame containing this frameview is currently active. Updated in
+  // ActivationChanged().
+  bool active_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(CustomFrameView);
 };