mash: Convert StatusAreaWidgetDelegate to wm common types

ash/mus/bridge/wm_shelf_mus.cc

Index: ash/mus/bridge/wm_shelf_mus.cc
diff --git a/ash/mus/bridge/wm_shelf_mus.cc b/ash/mus/bridge/wm_shelf_mus.cc
index 3153087cb3dd6aa90a2e4aec28cedcd8d60f456c..99610b92f922bbced3f233e314737a900ab92828 100644
--- a/ash/mus/bridge/wm_shelf_mus.cc
+++ b/ash/mus/bridge/wm_shelf_mus.cc
@@ -102,6 +102,12 @@ gfx::Rect WmShelfMus::GetScreenBoundsOfItemIconForWindow(WmWindow* window) {
   return gfx::Rect();
 }
 
+bool WmShelfMus::ProcessGestureEvent(const ui::GestureEvent& event,
+                                     WmWindow* target_window) {
+  NOTIMPLEMENTED();
+  return false;
+}
+
 void WmShelfMus::UpdateAutoHideForMouseEvent(ui::MouseEvent* event) {
   NOTIMPLEMENTED();
 }