Draggable peeking/fullscreen launcher with transparent background.

ash/shelf/app_list_button.cc

Index: ash/shelf/app_list_button.cc
diff --git a/ash/shelf/app_list_button.cc b/ash/shelf/app_list_button.cc
index 584d9d842d223fcaf91911116abcb9d32d96a0be..efecc294aa093c4b389fae44cf1998ee35148f06 100644
--- a/ash/shelf/app_list_button.cc
+++ b/ash/shelf/app_list_button.cc
@@ -44,7 +44,7 @@ AppListButton::AppListButton(InkDropButtonListener* listener,
   DCHECK(listener_);
   DCHECK(shelf_view_);
   DCHECK(shelf_);
-
+  Shell::Get()->AddShellObserver(this);
   SetInkDropMode(InkDropMode::ON_NO_GESTURE_HANDLER);
   set_ink_drop_base_color(kShelfInkDropBaseColor);
   set_ink_drop_visible_opacity(kShelfInkDropVisibleOpacity);
@@ -55,7 +55,9 @@ AppListButton::AppListButton(InkDropButtonListener* listener,
   set_notify_action(CustomButton::NOTIFY_ON_PRESS);
 }
 
-AppListButton::~AppListButton() {}
+AppListButton::~AppListButton() {
+  Shell::Get()->RemoveShellObserver(this);
+}
 
 void AppListButton::OnAppListShown() {
   AnimateInkDrop(views::InkDropState::ACTIVATED, nullptr);
@@ -239,4 +241,15 @@ gfx::Point AppListButton::GetCenterPoint() const {
   }
 }
 
+void AppListButton::OnAppListVisibilityChanged(bool shown,
+                                               aura::Window* root_window) {
+  if (shelf_ != Shelf::ForWindow(root_window))
+    return;
+
+  if (shown)
+    OnAppListShown();
+  else
+    OnAppListDismissed();
+}
+
 }  // namespace ash