Fixes bug in DesktopWindowTreeHostMus's activation handling

ui/views/mus/desktop_window_tree_host_mus.cc

Index: ui/views/mus/desktop_window_tree_host_mus.cc
diff --git a/ui/views/mus/desktop_window_tree_host_mus.cc b/ui/views/mus/desktop_window_tree_host_mus.cc
index 1b834c7d3f6e6de2308c696d833aabc0d0019bc0..e8dcb5b3a5e2c657cc662b7a27b2762d919704b5 100644
--- a/ui/views/mus/desktop_window_tree_host_mus.cc
+++ b/ui/views/mus/desktop_window_tree_host_mus.cc
@@ -531,13 +531,16 @@ void DesktopWindowTreeHostMus::SetShape(
 }
 
 void DesktopWindowTreeHostMus::Activate() {
+  if (!IsVisible())
+    return;
+
+  // This should result in OnActiveFocusClientChanged() being called, which
+  // triggers a call to DesktopNativeWidgetAura::HandleActivationChanged(),
+  // which focuses the right window.
   aura::Env::GetInstance()->SetActiveFocusClient(
       aura::client::GetFocusClient(window()), window());
-  if (is_active_) {
-    window()->Focus();

[sky, 2017/02/10 19:18:48]

The explicit call to Focus() isn't necessary here as HandleActivationChanged()
(called in OnActiveFocusClientChanged()) focuses the right window.

-    if (window()->GetProperty(aura::client::kDrawAttentionKey))
-      window()->SetProperty(aura::client::kDrawAttentionKey, false);
-  }
+  if (is_active_)
+    window()->SetProperty(aura::client::kDrawAttentionKey, false);
 }
 
 void DesktopWindowTreeHostMus::Deactivate() {