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..242166445aabfa8033da0533c37638c072724feb 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 +241,12 @@ gfx::Point AppListButton::GetCenterPoint() const {
   }
 }
 
+void AppListButton::OnAppListShownOrDismissed(bool shown,
+                                              aura::Window* root_window) {
+  if (shown)
+    OnAppListShown();
+  else
+    OnAppListDismissed();

[xiyuan, 2017/06/06 15:51:04]

This is not right on multiple monitors. AppListButton is per shelf and shelf is
per display. So this would cause all AppListButton on all displays to change its
status, which is not right.

We need to filter it by root window.

[newcomer, 2017/06/06 16:42:29]

Done.

+}
+
 }  // namespace ash