Change FocusSynchronizer to maintain active focus client and window.

ui/aura/client/aura_constants.cc

Index: ui/aura/client/aura_constants.cc
diff --git a/ui/aura/client/aura_constants.cc b/ui/aura/client/aura_constants.cc
index 46099a6684be184d3d7518fe9e9850d7d09db43a..1edf5a5d3de7350144fcad21d19d2c4a9a2996d6 100644
--- a/ui/aura/client/aura_constants.cc
+++ b/ui/aura/client/aura_constants.cc
@@ -23,6 +23,7 @@ DECLARE_EXPORTED_UI_CLASS_PROPERTY_TYPE(AURA_EXPORT, int32_t)
 DECLARE_EXPORTED_UI_CLASS_PROPERTY_TYPE(AURA_EXPORT, int64_t)
 DECLARE_EXPORTED_UI_CLASS_PROPERTY_TYPE(AURA_EXPORT,
                                         aura::client::WindowEmbedType)
+DECLARE_EXPORTED_UI_CLASS_PROPERTY_TYPE(AURA_EXPORT, aura::client::FocusClient*)
 
 namespace aura {
 namespace client {
@@ -39,6 +40,7 @@ DEFINE_UI_CLASS_PROPERTY_KEY(int, kAppType, 0);
 DEFINE_UI_CLASS_PROPERTY_KEY(bool, kConstrainedWindowKey, false);
 DEFINE_UI_CLASS_PROPERTY_KEY(bool, kCreatedByUserGesture, false);
 DEFINE_UI_CLASS_PROPERTY_KEY(bool, kDrawAttentionKey, false);
+DEFINE_UI_CLASS_PROPERTY_KEY(FocusClient*, kFocusClientKey, nullptr);
 DEFINE_UI_CLASS_PROPERTY_KEY(Window*, kHostWindowKey, nullptr);
 DEFINE_UI_CLASS_PROPERTY_KEY(bool, kImmersiveFullscreenKey, false);
 DEFINE_UI_CLASS_PROPERTY_KEY(bool, kMirroringEnabledKey, false);