Eliminate ash::Shell access in ShelfView

ash/common/wm_shell.h

Index: ash/common/wm_shell.h
diff --git a/ash/common/wm_shell.h b/ash/common/wm_shell.h
index 1cdc2c5b913deccffd8585d6848ab07de66eda46..38a91d04865a9b1e4e944840849bbe7aec5c5cff 100644
--- a/ash/common/wm_shell.h
+++ b/ash/common/wm_shell.h
@@ -15,6 +15,11 @@
 #include "ash/common/metrics/user_metrics_action.h"
 #include "ash/common/wm/lock_state_observer.h"
 #include "base/observer_list.h"
+#include "ui/base/ui_base_types.h"
+
+namespace gfx {
+class Point;
+}
 
 namespace views {
 class PointerWatcher;
@@ -204,6 +209,11 @@ class ASH_EXPORT WmShell {
   virtual void RecordUserMetricsAction(UserMetricsAction action) = 0;
   virtual void RecordTaskSwitchMetric(TaskSwitchSource source) = 0;
 
+  // Shows the context menu for the background and the shelf at
+  // |location_in_screen|.
+  virtual void ShowContextMenu(const gfx::Point& location_in_screen,
+                               ui::MenuSourceType source_type) = 0;
+
   // Returns a WindowResizer to handle dragging. |next_window_resizer| is
   // the next WindowResizer in the WindowResizer chain. This may return
   // |next_window_resizer|.