Implement "pinned" mode in ash.

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 1376d72dcc47cd2968021b137a46179239242ad9..78800a3823ba7d1edf0c239375f9e456e95f1fd2 100644
--- a/ash/shelf/shelf_layout_manager.cc
+++ b/ash/shelf/shelf_layout_manager.cc
@@ -313,6 +313,8 @@ void ShelfLayoutManager::UpdateVisibilityState() {
 
   if (state_.is_screen_locked || state_.is_adding_user_screen) {
     SetState(SHELF_VISIBLE);
+  } else if (WmShell::Get()->IsPinned()) {
+    SetState(SHELF_HIDDEN);
   } else {
     // TODO(zelidrag): Verify shelf drag animation still shows on the device
     // when we are in SHELF_AUTO_HIDE_ALWAYS_HIDDEN.
@@ -549,6 +551,12 @@ void ShelfLayoutManager::OnShelfAutoHideBehaviorChanged(WmWindow* root_window) {
   UpdateVisibilityState();
 }
 
+void ShelfLayoutManager::OnPinnedStateChanged(WmWindow* pinned_window) {
+  // Shelf needs to be hidden on entering to pinned mode, or restored
+  // on exiting from pinned mode.
+  UpdateVisibilityState();
+}
+
 void ShelfLayoutManager::OnWindowActivated(
     aura::client::ActivationChangeObserver::ActivationReason reason,
     aura::Window* gained_active,