Moves WorkspaceEventHandler to ash/common

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 2129ba1dd4244c1d2eb6443429a765bd3937fbae..5021ee0c5a02032436bd05418ff996da543f14d0 100644
--- a/ash/aura/wm_shell_aura.cc
+++ b/ash/aura/wm_shell_aura.cc
@@ -27,6 +27,7 @@
 #include "ash/wm/screen_pinning_controller.h"
 #include "ash/wm/window_cycle_event_filter_aura.h"
 #include "ash/wm/window_util.h"
+#include "ash/wm/workspace/workspace_event_handler_aura.h"
 #include "base/memory/ptr_util.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/aura/client/focus_client.h"
@@ -203,6 +204,11 @@ WmShellAura::CreateMaximizeModeEventHandler() {
   return base::WrapUnique(new wm::MaximizeModeEventHandlerAura);
 }
 
+std::unique_ptr<WorkspaceEventHandler> WmShellAura::CreateWorkspaceEventHandler(
+    WmWindow* workspace_window) {
+  return base::MakeUnique<WorkspaceEventHandlerAura>(workspace_window);
+}
+
 std::unique_ptr<ScopedDisableInternalMouseAndKeyboard>
 WmShellAura::CreateScopedDisableInternalMouseAndKeyboard() {
 #if defined(USE_X11)