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..b9dc54f5da98cf0966856a8111e16d56f611ee5b 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 (state_.is_pinned) {
+    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 +551,11 @@ void ShelfLayoutManager::OnShelfAutoHideBehaviorChanged(WmWindow* root_window) {
   UpdateVisibilityState();
 }
 
+void ShelfLayoutManager::OnPinnedStateChanged(WmWindow* pinned_window) {
+  state_.is_pinned = pinned_window->GetWindowState()->IsPinned();
+  UpdateVisibilityState();
+}
+
 void ShelfLayoutManager::OnWindowActivated(
     aura::client::ActivationChangeObserver::ActivationReason reason,
     aura::Window* gained_active,
@@ -586,6 +593,7 @@ void ShelfLayoutManager::SetState(ShelfVisibilityState visibility_state) {
   // Preserve the log in screen states.
   state.is_adding_user_screen = state_.is_adding_user_screen;
   state.is_screen_locked = state_.is_screen_locked;
+  state.is_pinned = state_.is_pinned;
 
   // Force an update because gesture drags affect the shelf bounds and we
   // should animate back to the normal bounds at the end of a gesture.