aura-mus: Implement Deactivate().

ui/aura/mus/window_tree_host_mus.cc

Index: ui/aura/mus/window_tree_host_mus.cc
diff --git a/ui/aura/mus/window_tree_host_mus.cc b/ui/aura/mus/window_tree_host_mus.cc
index ba6e05f5e07346442d76eb37c7b5b6803ee46d67..2edd659db0f576d7a18742b7b5e19daf12e49a2a 100644
--- a/ui/aura/mus/window_tree_host_mus.cc
+++ b/ui/aura/mus/window_tree_host_mus.cc
@@ -117,6 +117,10 @@ void WindowTreeHostMus::SetHitTestMask(const base::Optional<gfx::Rect>& rect) {
   delegate_->OnWindowTreeHostHitTestMaskWillChange(this, rect);
 }
 
+void WindowTreeHostMus::ClearFocus() {
+  delegate_->OnWindowTreeHostClearFocus();
+}

[Elliot Glaysher, 2016/12/13 23:30:20]

I don't like this emerging pattern. DesktopWindowTreeHostMus calls this method
through its base class which calls WindowTreeClient through a delegate
interface. Seems like a lot of forwarding for a simple thing.

+
 display::Display WindowTreeHostMus::GetDisplay() const {
   for (const display::Display& display :
        display::Screen::GetScreen()->GetAllDisplays()) {