Added common layout framework for system menu rows.

ash/common/system/tray/size_range_layout.h

+// 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 "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 to override the preferred size of an ImageView that would
+//  have a preferred size of (25, 25) to have a size of (50, 50).
+//
+// Example code:
+//
+//  ImageView* image_view = new ImageView();
+//  image_view->SetImage(image); // Where |image| has a size of (25, 25).
+//  SizeRangeLayout* layout = new SizeRangeLayout();
+//  layout->SetSize(gfx::Size(50, 50));
+//  image_view->SetLayoutManager(layout);
+//
+class SizeRangeLayout : public views::LayoutManager {

[sky, 2016/10/14 22:11:12]

Unless I'm missing something this class seems problematic. It isn't uncommon for
views you may want to use with this class to override functions that go to the
LayoutManager. Even the example you give doesn't work as ImageView overrides
GetPreferredSize.

[bruthig, 2016/10/17 15:53:12]

Ah right, I guess I need to update the example code to wrap the ImageView in a
raw container View and apply the layout manager to the container view.

+ public:
+  // The minimum width/height.
+  static const int kMinSize;
+
+  // The maximum width/height.
+  static const int kMaxSize;
+
+  // Returns the minimum possible size. Use this with set_min_size() to
+  // effectively unset the minimum preferred size.
+  static gfx::Size MinSize();
+
+  // Returns the maximum possible size. Use this with set_max_size() to
+  // effectively unset the maximum preferred size.
+  static gfx::Size MaxSize();
+
+  // Create a layout with no minimum or maximum preferred size.
+  SizeRangeLayout();
+
+  // Create a layout with the given minimum and maximum preferred sizes.
+  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);
+
+  void set_min_size(const gfx::Size& size) { min_size_ = size; }
+  void set_max_size(const gfx::Size& size) { max_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 Uninstalled(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:
+  // 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_