Moves WorkspaceEventHandler to ash/common

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 2c9bad3ff8de174c0556f3d18787d90622499897..f311fda5ae8f090d24262f6601534366cbd1b40d 100644
--- a/ash/mus/bridge/wm_shell_mus.cc
+++ b/ash/mus/bridge/wm_shell_mus.cc
@@ -26,6 +26,7 @@
 #include "ash/mus/bridge/immersive_handler_factory_mus.h"
 #include "ash/mus/bridge/wm_root_window_controller_mus.h"
 #include "ash/mus/bridge/wm_window_mus.h"
+#include "ash/mus/bridge/workspace_event_handler_mus.h"
 #include "ash/mus/container_ids.h"
 #include "ash/mus/drag_window_resizer.h"
 #include "ash/mus/root_window_controller.h"
@@ -345,6 +346,12 @@ WmShellMus::CreateScopedDisableInternalMouseAndKeyboard() {
   return nullptr;
 }
 
+std::unique_ptr<WorkspaceEventHandler> WmShellMus::CreateWorkspaceEventHandler(
+    WmWindow* workspace_window) {
+  return base::MakeUnique<WorkspaceEventHandlerMus>(
+      WmWindowMus::GetMusWindow(workspace_window));
+}
+
 std::unique_ptr<ImmersiveFullscreenController>
 WmShellMus::CreateImmersiveFullscreenController() {
   return base::MakeUnique<ImmersiveFullscreenController>();