Attempt to re-land FocusManager removal from Aura.

ui/aura/root_window.cc

Index: ui/aura/root_window.cc
diff --git a/ui/aura/root_window.cc b/ui/aura/root_window.cc
index 19c60bf62bee4b506e00397a2e82145daa59f95d..bfd6b3500a46a13714b0c8c5db2541e3aca34ba6 100644
--- a/ui/aura/root_window.cc
+++ b/ui/aura/root_window.cc
@@ -11,7 +11,6 @@
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
-#include "ui/aura/client/activation_client.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/aura/client/cursor_client.h"
 #include "ui/aura/client/event_client.h"
@@ -706,12 +705,6 @@ void RootWindow::OnWindowRemovedFromRootWindow(Window* detached,
 }
 
 void RootWindow::OnWindowHidden(Window* invisible, WindowHiddenReason reason) {
-  // TODO(beng): This should be removed once FocusController is turned on.
-  if (client::GetFocusClient(this)) {
-    client::GetFocusClient(this)->OnWindowHiddenInRootWindow(
-        invisible, this, reason == WINDOW_DESTROYED);
-  }
-
   // Do not clear the capture, and the |event_dispatch_target_| if the
   // window is moving across root windows, because the target itself
   // is actually still visible and clearing them stops further event