Refactors maximize mode event handling into its own class

ash/mus/bridge/wm_shell_mus.cc

Index: ash/mus/bridge/wm_shell_mus.cc
diff --git a/ash/mus/bridge/wm_shell_mus.cc b/ash/mus/bridge/wm_shell_mus.cc
index 35d736110fbaf25a40e2a89ca0911d39ed4d0eb1..4660fd34f34d4386a45133a6726aa2894da77559 100644
--- a/ash/mus/bridge/wm_shell_mus.cc
+++ b/ash/mus/bridge/wm_shell_mus.cc
@@ -10,6 +10,7 @@
 #include "ash/common/shell_observer.h"
 #include "ash/common/shell_window_ids.h"
 #include "ash/common/system/tray/default_system_tray_delegate.h"
+#include "ash/common/wm/maximize_mode/maximize_mode_event_handler.h"
 #include "ash/common/wm/mru_window_tracker.h"
 #include "ash/common/wm/window_resizer.h"
 #include "ash/common/wm_activation_observer.h"
@@ -230,6 +231,14 @@ std::unique_ptr<WindowResizer> WmShellMus::CreateDragWindowResizer(
       new DragWindowResizer(std::move(next_window_resizer), window_state));
 }
 
+std::unique_ptr<wm::MaximizeModeEventHandler>
+WmShellMus::CreateMaximizeModeEventHandler() {
+  // TODO: need support for window manager to get events before client:
+  // http://crbug.com/624157.
+  NOTIMPLEMENTED();
+  return nullptr;
+}
+
 void WmShellMus::OnOverviewModeStarting() {
   FOR_EACH_OBSERVER(ShellObserver, *wm_shell_common_->shell_observers(),
                     OnOverviewModeStarting());