Updates shadow when active window changes

components/mus/public/cpp/lib/window_tree_client_impl.cc

Index: components/mus/public/cpp/lib/window_tree_client_impl.cc
diff --git a/components/mus/public/cpp/lib/window_tree_client_impl.cc b/components/mus/public/cpp/lib/window_tree_client_impl.cc
index 2b094e96cdc0aa071aa8b3cd18e2d40e3d0b7f0d..2ae19a1a466b5d3bddd9d56c12fec0412e3f3778 100644
--- a/components/mus/public/cpp/lib/window_tree_client_impl.cc
+++ b/components/mus/public/cpp/lib/window_tree_client_impl.cc
@@ -11,6 +11,7 @@
 #include "components/mus/public/cpp/window_manager_delegate.h"
 #include "components/mus/public/cpp/window_observer.h"
 #include "components/mus/public/cpp/window_tree_connection.h"
+#include "components/mus/public/cpp/window_tree_connection_observer.h"
 #include "components/mus/public/cpp/window_tree_delegate.h"
 #include "mojo/application/public/cpp/application_impl.h"
 #include "mojo/application/public/cpp/connect.h"
@@ -353,6 +354,11 @@ void WindowTreeClientImpl::OnEmbedImpl(mojom::WindowTree* window_tree,
   focused_window_ = GetWindowById(focused_window_id);
 
   delegate_->OnEmbed(root_);
+
+  if (focused_window_) {
+    FOR_EACH_OBSERVER(WindowTreeConnectionObserver, observers_,
+                      OnWindowTreeFocusChanged(focused_window_, nullptr));
+  }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -402,6 +408,15 @@ ConnectionSpecificId WindowTreeClientImpl::GetConnectionId() {
 ////////////////////////////////////////////////////////////////////////////////
 // WindowTreeClientImpl, WindowTreeClient implementation:
 
+void WindowTreeClientImpl::AddObserver(WindowTreeConnectionObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void WindowTreeClientImpl::RemoveObserver(
+    WindowTreeConnectionObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
 void WindowTreeClientImpl::OnEmbed(ConnectionSpecificId connection_id,
                                    mojom::WindowDataPtr root_data,
                                    mojom::WindowTreePtr tree,
@@ -595,6 +610,8 @@ void WindowTreeClientImpl::OnWindowFocused(Id focused_window_id) {
     FOR_EACH_OBSERVER(WindowObserver, *WindowPrivate(focused).observers(),
                       OnWindowFocusChanged(focused, blurred));
   }
+  FOR_EACH_OBSERVER(WindowTreeConnectionObserver, observers_,
+                    OnWindowTreeFocusChanged(focused, blurred));
 }
 
 void WindowTreeClientImpl::OnChangeCompleted(uint32 change_id, bool success) {