Refactors maximize mode event handling into its own class

ash/aura/wm_shell_aura.cc

Index: ash/aura/wm_shell_aura.cc
diff --git a/ash/aura/wm_shell_aura.cc b/ash/aura/wm_shell_aura.cc
index 10c33cadb1dc954fa58a95dedcf49c2791557260..ba029b59a483bffb40787bee61bf4271c227623c 100644
--- a/ash/aura/wm_shell_aura.cc
+++ b/ash/aura/wm_shell_aura.cc
@@ -17,6 +17,7 @@
 #include "ash/shell.h"
 #include "ash/shell_delegate.h"
 #include "ash/wm/drag_window_resizer.h"
+#include "ash/wm/maximize_mode/maximize_mode_event_handler_aura.h"
 #include "ash/wm/screen_pinning_controller.h"
 #include "ash/wm/window_util.h"
 #include "base/memory/ptr_util.h"
@@ -128,6 +129,11 @@ std::unique_ptr<WindowResizer> WmShellAura::CreateDragWindowResizer(
       DragWindowResizer::Create(next_window_resizer.release(), window_state));
 }
 
+std::unique_ptr<wm::MaximizeModeEventHandler>
+WmShellAura::CreateMaximizeModeEventHandler() {
+  return base::WrapUnique(new wm::MaximizeModeEventHandlerAura);
+}
+
 void WmShellAura::OnOverviewModeStarting() {
   FOR_EACH_OBSERVER(ShellObserver, *wm_shell_common_->shell_observers(),
                     OnOverviewModeStarting());