Added common layout framework for system menu rows.

ash/common/system/tray/size_range_layout.h

Index: ash/common/system/tray/size_range_layout.h
diff --git a/ash/common/system/tray/size_range_layout.h b/ash/common/system/tray/size_range_layout.h
new file mode 100644
index 0000000000000000000000000000000000000000..175960f63bfda04653cca8b3c926252b8b95b004
--- /dev/null
+++ b/ash/common/system/tray/size_range_layout.h
@@ -0,0 +1,112 @@
+// 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_SIZE_RANGE_LAYOUT_H_
+#define ASH_COMMON_SYSTEM_TRAY_SIZE_RANGE_LAYOUT_H_
+
+#include <memory>
+
+#include "ash/ash_export.h"
+#include "base/macros.h"
+#include "ui/gfx/geometry/size.h"
+#include "ui/views/layout/layout_manager.h"
+
+namespace views {
+class View;
+}  // namespace views
+
+namespace ash {
+
+// A LayoutManager adapter that allows clients to specify a minimum and/or a
+// maximum preferred size. The actual layout will be delegated to the
+// LayoutManager owned by this. i.e. |this| can be used to override the
+// preferred size returned by a View.
+//
+// By default the SizeRangeLayout is configured to own a FillLayout but this can
+// be overridden with SetLayoutManager().
+//
+// Example use case :
+//
+//  Suppose you wanted a Label to take up a specific size of (50, 50) even
+//  though the label's preferred size was (25, 25).
+//
+// Example code:
+//
+//  Label* label = new Label(kSomeDummyText);
+//  View* container = new View();
+//  container->AddChildView(label);
+//  SizeRangeLayout* layout = new SizeRangeLayout();
+//  layout->SetSize(gfx::Size(50, 50));
+//  container->SetLayoutManager(layout);
+//
+class ASH_EXPORT SizeRangeLayout : public views::LayoutManager {
+ public:
+  // Returns the absolute minimum possible size. Use this with set_min_size() to
+  // effectively unset the minimum preferred size.
+  static gfx::Size AbsoluteMinSize();
+
+  // Returns the absolute maximum possible size. Use this with set_max_size() to
+  // effectively unset the maximum preferred size.
+  static gfx::Size AbsoluteMaxSize();
+
+  // Create a layout with no minimum or maximum preferred size.
+  SizeRangeLayout();
+
+  // Create a layout with the given minimum and maximum preferred sizes. If
+  // |max_size| is smaller than |min_size| then |min_size| will be set to the
+  // smaller |max_size| value.
+  SizeRangeLayout(const gfx::Size& min_size, const gfx::Size& max_size);
+
+  ~SizeRangeLayout() override;
+
+  // Sets both the minimum and maximum preferred size.
+  void SetSize(const gfx::Size& size);
+
+  // Set the minimum preferred size that GetPreferredSize() will round up to. If
+  // |size| is larger than the current |max_size_| then |max_size_| will set to
+  // |size| as well.
+  void SetMinSize(const gfx::Size& size);
+
+  // Set the minimum preferred size that GetPreferredSize() will round down to.
+  // If |size| is smaller than the current |min_size_| then |min_size_| will set
+  // to |size| as well.
+  void SetMaxSize(const gfx::Size& size);
+
+  // Sets the layout manager that actually performs the layout once the bounds
+  // have been defined.
+  void SetLayoutManager(std::unique_ptr<LayoutManager> layout_manager);
+
+  // LayoutManager:
+  void Installed(views::View* host) override;
+  void Layout(views::View* host) override;
+  gfx::Size GetPreferredSize(const views::View* host) const override;
+  int GetPreferredHeightForWidth(const views::View* host,
+                                 int width) const override;
+  void ViewAdded(views::View* host, views::View* view) override;
+  void ViewRemoved(views::View* host, views::View* view) override;
+
+ private:
+  friend class SizeRangeLayoutTest;
+
+  // Clamps |size| to be within the minimum and maximum preferred sizes.
+  void ClampSizeToRange(gfx::Size* size) const;
+
+  // The host View that this has been installed on.
+  views::View* host_ = nullptr;
+
+  // The layout manager that actually performs the layout.
+  std::unique_ptr<views::LayoutManager> layout_manager_;
+
+  // The minimum preferred size.
+  gfx::Size min_size_;
+
+  // The maximum preferred size.
+  gfx::Size max_size_;
+
+  DISALLOW_COPY_AND_ASSIGN(SizeRangeLayout);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_SYSTEM_TRAY_SIZE_RANGE_LAYOUT_H_