mus: Allow the WM to specify the windows that can have active children.

components/mus/ws/focus_controller_unittest.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/mus/ws/focus_controller.h"
 
 #include "components/mus/ws/focus_controller_delegate.h"
 #include "components/mus/ws/server_window.h"
 #include "components/mus/ws/test_server_window_delegate.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 14 matching lines @@
     change_count_ = 0u;
     old_focused_window_ = nullptr;
     new_focused_window_ = nullptr;
   }
   size_t change_count() const { return change_count_; }
   ServerWindow* old_focused_window() { return old_focused_window_; }
   ServerWindow* new_focused_window() { return new_focused_window_; }
 
  private:
   // FocusControllerDelegate:
+  bool CanHaveActiveChildren(ServerWindow* window) const override {
+    return true;
+  }
+  void OnActivationChanged(ServerWindow* old_active_window,
+                           ServerWindow* new_active_window) override {}
   void OnFocusChanged(ServerWindow* old_focused_window,
                       ServerWindow* new_focused_window) override {
     change_count_++;
     old_focused_window_ = old_focused_window;
     new_focused_window_ = new_focused_window;
   }
 
   size_t change_count_;
   ServerWindow* old_focused_window_;
   ServerWindow* new_focused_window_;
@@ skipping 57 matching lines @@
   child.SetVisible(false);
   EXPECT_EQ(1u, focus_delegate.change_count());
   EXPECT_EQ(&root, focus_delegate.new_focused_window());
   EXPECT_EQ(&child_child, focus_delegate.old_focused_window());
   focus_delegate.ClearAll();
 }
 
 }  // namespace ws
 
 }  // namespace mus