Draggable peeking/fullscreen launcher with transparent background.

ash/shelf/shelf_layout_manager.cc

Index: ash/shelf/shelf_layout_manager.cc
diff --git a/ash/shelf/shelf_layout_manager.cc b/ash/shelf/shelf_layout_manager.cc
index 429fd15c7004dc7cdd2bbb55fcea370701db4416..9a423c0dac5e8ac1be420fffa4db015355a8543f 100644
--- a/ash/shelf/shelf_layout_manager.cc
+++ b/ash/shelf/shelf_layout_manager.cc
@@ -173,6 +173,11 @@ ShelfLayoutManager::~ShelfLayoutManager() {
   ShellPort::Get()->RemoveLockStateObserver(this);
 }
 
+void ShelfLayoutManager::OnAppListIsActive(bool is_active) {
+  app_list_is_active_ = is_active;

[sky, 2017/05/31 15:04:17]

Is it really necessary to cache this state? Could it be looked up when
necessary?

[newcomer, 2017/06/01 01:42:54]

Done.

+  MaybeUpdateShelfBackground(AnimationChangeType::IMMEDIATE);
+}
+
 void ShelfLayoutManager::PrepareForShutdown() {
   in_shutdown_ = true;
   // Stop observing changes to avoid updating a partially destructed shelf.
@@ -468,6 +473,10 @@ ShelfBackgroundType ShelfLayoutManager::GetShelfBackgroundType() const {
   if (state_.session_state != session_manager::SessionState::ACTIVE)
     return SHELF_BACKGROUND_OVERLAP;
 
+  // If the app list is active, hide the shelf background to prevent overlap.
+  if (app_list_is_active_)
+    return SHELF_BACKGROUND_DEFAULT;
+
   if (state_.visibility_state != SHELF_AUTO_HIDE &&
       state_.window_state == wm::WORKSPACE_WINDOW_STATE_MAXIMIZED) {
     return SHELF_BACKGROUND_MAXIMIZED;