Draggable peeking/fullscreen launcher with transparent background.

ash/shelf/app_list_button.h

Index: ash/shelf/app_list_button.h
diff --git a/ash/shelf/app_list_button.h b/ash/shelf/app_list_button.h
index 02c69c22807a47f39985515746ba186897246e25..4acfcad93d6e1338b79d6d01b84301b96dd3f141 100644
--- a/ash/shelf/app_list_button.h
+++ b/ash/shelf/app_list_button.h
@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "ash/ash_export.h"
+#include "ash/shell_observer.h"
 #include "base/macros.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/views/controls/button/image_button.h"
@@ -18,7 +19,8 @@ class Shelf;
 class ShelfView;
 
 // Button used for the AppList icon on the shelf.
-class ASH_EXPORT AppListButton : public views::ImageButton {
+class ASH_EXPORT AppListButton : public views::ImageButton,
+                                 public ShellObserver {
  public:
   AppListButton(InkDropButtonListener* listener,
                 ShelfView* shelf_view,
@@ -55,6 +57,10 @@ class ASH_EXPORT AppListButton : public views::ImageButton {
   // ink drops.
   gfx::Point GetCenterPoint() const;
 
+  // ShellObserver overrides:
+  void OnAppListShownOrDismissed(bool shown,
+                                 aura::Window* root_window) override;
+
   // True if the app list is currently showing for this display.
   // This is useful because other IsApplistVisible functions aren't per-display.
   bool is_showing_app_list_;