Added common layout framework for system menu rows.

ash/common/system/tray/tray_popup_layout_factory.h

Index: ash/common/system/tray/tray_popup_layout_factory.h
diff --git a/ash/common/system/tray/tray_popup_layout_factory.h b/ash/common/system/tray/tray_popup_layout_factory.h
new file mode 100644
index 0000000000000000000000000000000000000000..5e5669eb93d48fe182ab829f34503c081505947d
--- /dev/null
+++ b/ash/common/system/tray/tray_popup_layout_factory.h
@@ -0,0 +1,55 @@
+// 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.
+
+#ifndef ASH_COMMON_SYSTEM_TRAY_TRAY_POPUP_LAYOUT_FACTORY_H_
+#define ASH_COMMON_SYSTEM_TRAY_TRAY_POPUP_LAYOUT_FACTORY_H_
+
+#include <memory>
+
+#include "ash/common/system/tray/three_view_layout.h"
+#include "base/macros.h"
+
+namespace views {
+class View;
+}  // namespace views
+
+namespace ash {
+
+// Factory functions for system menu row layout managers.
+class TrayPopupLayoutFactory {
+ public:
+  // Sets the layout manager of |host| to the default layout manager used by
+  // most system menu rows. The newly created layout manager is owned by the
+  // |host| but is returned so child Views can be added.
+  //
+  // The returned layout manager consists of 3 regions: START, CENTER, and END.
+  // Any child Views added to the START and END containers will be added
+  // horizonatlly and any Views added to the CENTER container will be added
+  // vertically.
+  //
+  // The START and END containers have a fixed width but can grow into the
+  // CENTER container if space is required and available.
+  //
+  // The CENTER container has a flexible width.
+  static ThreeViewLayout* InstallDefaultLayout(views::View* host);
+
+  // Configures the different |container| Views with the default layout
+  // managers.
+  //
+  // This can be used by clients who need to embed portions of the default
+  // layout manager into a different container view, e.g. just the END layout
+  // into a clickable View.
+  static void ConfigureDefaultLayout(ThreeViewLayout* layout,
+                                     ThreeViewLayout::Container container);
+
+ private:
+  TrayPopupLayoutFactory();
+  ~TrayPopupLayoutFactory();
+
+  DISALLOW_COPY_AND_ASSIGN(TrayPopupLayoutFactory);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_SYSTEM_TRAY_TRAY_POPUP_LAYOUT_FACTORY_H_