(Merge to M-51) Revise the shelf alignment locking mechanism.

ash/shelf/shelf_locking_manager.cc

Index: ash/shelf/shelf_locking_manager.cc
diff --git a/ash/shelf/shelf_locking_manager.cc b/ash/shelf/shelf_locking_manager.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d291da6dc270092eceab4b2af6524a0f66f4ddf7
--- /dev/null
+++ b/ash/shelf/shelf_locking_manager.cc
@@ -0,0 +1,62 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ash/shelf/shelf_locking_manager.h"
+
+#include "ash/session/session_state_delegate.h"
+#include "ash/shelf/shelf.h"
+#include "ash/shell.h"
+#include "ash/wm/lock_state_controller.h"
+
+namespace ash {
+
+ShelfLockingManager::ShelfLockingManager(Shelf* shelf) : shelf_(shelf) {
+  Shell* shell = Shell::GetInstance();
+  shell->lock_state_controller()->AddObserver(this);
+  SessionStateDelegate* delegate = shell->session_state_delegate();
+  session_locked_ =
+      delegate->GetSessionState() != SessionStateDelegate::SESSION_STATE_ACTIVE;
+  screen_locked_ = delegate->IsScreenLocked();
+  delegate->AddSessionStateObserver(this);
+  shell->AddShellObserver(this);
+}
+
+ShelfLockingManager::~ShelfLockingManager() {
+  Shell* shell = Shell::GetInstance();
+  shell->lock_state_controller()->RemoveObserver(this);
+  shell->session_state_delegate()->RemoveSessionStateObserver(this);
+  shell->RemoveShellObserver(this);
+}
+
+void ShelfLockingManager::OnLockStateChanged(bool locked) {
+  screen_locked_ = locked;
+  UpdateLockedState();
+}
+
+void ShelfLockingManager::SessionStateChanged(
+    SessionStateDelegate::SessionState state) {
+  session_locked_ = state != SessionStateDelegate::SESSION_STATE_ACTIVE;
+  UpdateLockedState();
+}
+
+void ShelfLockingManager::OnLockStateEvent(EventType event) {
+  // This is only called when locking the screen; there is no unlock event here.
+  // It's also called when the screen lock animation begins and should help the
+  // shelf appear locked much earlier than ShellObserver::OnLockStateChanged.
+  screen_locked_ = true;
+  UpdateLockedState();
+}
+
+void ShelfLockingManager::UpdateLockedState() {
+  const bool should_be_locked = screen_locked_ || session_locked_;
+  const ShelfAlignment alignment = shelf_->alignment();
+  if (should_be_locked && alignment != SHELF_ALIGNMENT_BOTTOM_LOCKED) {
+    stored_alignment_ = alignment;
+    shelf_->SetAlignment(SHELF_ALIGNMENT_BOTTOM_LOCKED);
+  } else if (!should_be_locked && alignment == SHELF_ALIGNMENT_BOTTOM_LOCKED) {
+    shelf_->SetAlignment(stored_alignment_);
+  }
+}
+
+}  // namespace ash