Implement a callout widget for the active panel.

ash/wm/panel_layout_manager.h

Index: ash/wm/panel_layout_manager.h
diff --git a/ash/wm/panel_layout_manager.h b/ash/wm/panel_layout_manager.h
index 11f9502c59410c8afaa9d8b69a1cd6ca933bf454..2b1f76d1cbc62b6f1e198b1db9bff7aae63bbcfa 100644
--- a/ash/wm/panel_layout_manager.h
+++ b/ash/wm/panel_layout_manager.h
@@ -12,6 +12,8 @@
 #include "ash/launcher/launcher_icon_observer.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
 #include "ui/aura/layout_manager.h"
 #include "ui/aura/window_observer.h"
 
@@ -23,6 +25,10 @@ namespace gfx {
 class Rect;
 }
 
+namespace views {
+class Widget;
+}
+
 namespace ash {
 class Launcher;
 
@@ -78,6 +84,17 @@ class ASH_EXPORT PanelLayoutManager : public aura::LayoutManager,
   // changes or a panel is moved).
   void UpdateStacking(aura::Window* active_panel);
 
+  // Trigger a delayed task to update the callout. We use this because
+  // otherwise, ShadowController::OnWindowPropertyChanged may be invoked after
+  // we've already updated the callout, causing the drop shadow to be stacked on
+  // top of the callout rather than the other way around.
+  // TODO(dcheng): Possibly a bug in the shadow controller. If a window is
+  // focused but not stacked at the top, I don't think its shadow should be
+  // drawn on top of "higher" windows.
+  void UpdateCallout(aura::Window* active_window);
+  // Don't call this directly. Only UpdateCallout() should call this method.

[sky, 2012/04/27 15:42:42]

nit: newline between 94/95. In fact typical style is newline between all members
below too.

+  void ShowCalloutHelper(aura::Window* active_panel);
+
   // Parent window associated with this layout manager.
   aura::Window* panel_container_;
   // Protect against recursive calls to Relayout().
@@ -91,6 +108,9 @@ class ASH_EXPORT PanelLayoutManager : public aura::LayoutManager,
   // The last active panel. Used to maintain stacking even if no panels are
   // currently focused.
   aura::Window* last_active_panel_;
+  // Manage the callout for the focused panel, if any.
+  scoped_ptr<views::Widget> callout_widget_;
+  base::WeakPtrFactory<PanelLayoutManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PanelLayoutManager);
 };