Makes WindowTree::SetFocus(null) work

ui/views/mus/native_widget_mus.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 "ui/views/mus/native_widget_mus.h"
 
 #include "base/macros.h"
 #include "base/thread_task_runner_handle.h"
 #include "components/mus/public/cpp/property_type_converters.h"
 #include "components/mus/public/cpp/window.h"
@@ skipping 672 matching lines @@
   // TODO(beng): this should probably be wired thru PlatformWindow.
   return window_ && window_->visible();
 }
 
 void NativeWidgetMus::Activate() {
   if (window_tree_host_)
     window_tree_host_->platform_window()->Activate();
 }
 
 void NativeWidgetMus::Deactivate() {
-  // NOTIMPLEMENTED();
+  if (IsActive())
+    window_->connection()->ClearFocus();
 }
 
 bool NativeWidgetMus::IsActive() const {
-  // NOTIMPLEMENTED();
-  return true;
+  mus::Window* focused =
+      window_ ? window_->connection()->GetFocusedWindow() : nullptr;
+  return focused && window_->Contains(focused);
 }
 
 void NativeWidgetMus::SetAlwaysOnTop(bool always_on_top) {
   // NOTIMPLEMENTED();
 }
 
 bool NativeWidgetMus::IsAlwaysOnTop() const {
   // NOTIMPLEMENTED();
   return false;
 }
@@ skipping 91 matching lines @@
   window_tree_host_->platform_window()->SetCursorById(
       mus::mojom::Cursor(cursor.native_type()));
 }
 
 bool NativeWidgetMus::IsMouseEventsEnabled() const {
   // NOTIMPLEMENTED();
   return true;
 }
 
 void NativeWidgetMus::ClearNativeFocus() {
-  // NOTIMPLEMENTED();
+  if (!IsActive())
+    return;
+  mus::Window* focused =
+      window_ ? window_->connection()->GetFocusedWindow() : nullptr;
+  if (focused && window_->Contains(focused) && focused != window_)
+    window_->SetFocus();
 }
 
 gfx::Rect NativeWidgetMus::GetWorkAreaBoundsInScreen() const {
   // NOTIMPLEMENTED();
   return gfx::Rect();
 }
 
 Widget::MoveLoopResult NativeWidgetMus::RunMoveLoop(
     const gfx::Vector2d& drag_offset,
     Widget::MoveLoopSource source,
@@ skipping 177 matching lines @@
     window_tree_host_->Show();
     GetNativeWindow()->Show();
   } else {
     window_tree_host_->Hide();
     GetNativeWindow()->Hide();
   }
   native_widget_delegate_->OnNativeWidgetVisibilityChanged(window->visible());
 }
 
 }  // namespace views