Moves TransientWindowClient to ui/aura/client and adds observer

ui/wm/core/focus_controller_unittest.cc

Index: ui/wm/core/focus_controller_unittest.cc
diff --git a/ui/wm/core/focus_controller_unittest.cc b/ui/wm/core/focus_controller_unittest.cc
index c0786b7b558c9fe961341ef01b21e8b56c47fb52..110a47c8454cd6cf43687b2a9cecb997fe8d615d 100644
--- a/ui/wm/core/focus_controller_unittest.cc
+++ b/ui/wm/core/focus_controller_unittest.cc
@@ -23,7 +23,6 @@
 #include "ui/events/test/event_generator.h"
 #include "ui/wm/core/base_focus_rules.h"
 #include "ui/wm/core/window_util.h"
-#include "ui/wm/core/wm_state.h"
 #include "ui/wm/public/activation_change_observer.h"
 #include "ui/wm/public/activation_client.h"
 
@@ -372,7 +371,6 @@ class FocusControllerTestBase : public aura::test::AuraTestBase {
 
   // Overridden from aura::test::AuraTestBase:
   void SetUp() override {
-    wm_state_.reset(new wm::WMState);
     // FocusController registers itself as an Env observer so it can catch all
     // window initializations, including the root_window()'s, so we create it
     // before allowing the base setup.
@@ -419,7 +417,6 @@ class FocusControllerTestBase : public aura::test::AuraTestBase {
     aura::test::AuraTestBase::TearDown();
     test_focus_rules_ = NULL;  // Owned by FocusController.
     focus_controller_.reset();
-    wm_state_.reset();
   }
 
   void FocusWindow(aura::Window* window) {
@@ -472,7 +469,6 @@ class FocusControllerTestBase : public aura::test::AuraTestBase {
  private:
   std::unique_ptr<FocusController> focus_controller_;
   TestFocusRules* test_focus_rules_;
-  std::unique_ptr<wm::WMState> wm_state_;
 
   DISALLOW_COPY_AND_ASSIGN(FocusControllerTestBase);
 };