views: add layout delegates

chrome/browser/ui/views/harmony/layout_delegate.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 CHROME_BROWSER_UI_VIEWS_HARMONY_LAYOUT_DELEGATE_H_
+#define CHROME_BROWSER_UI_VIEWS_HARMONY_LAYOUT_DELEGATE_H_
+
+#include "ui/views/layout/grid_layout.h"
+
+class LayoutDelegate {
+ public:
+  enum class LayoutDistanceType {
+    PANEL_VERT_MARGIN,
+    RELATED_CONTROL_HORIZONTAL_SPACING,
+    RELATED_CONTROL_VERTICAL_SPACING,
+    RELATED_BUTTON_HORIZONTAL_SPACING,
+    UNRELATED_CONTROL_VERTICAL_SPACING,
+    UNRELATED_CONTROL_LARGE_VERTICAL_SPACING,
+    BUTTON_HEDGE_MARGIN_NEW,
+    BUTTON_VEDGE_MARGIN_NEW,
+  };
+
+  LayoutDelegate() {}
+  virtual ~LayoutDelegate() {}
+
+  // Returns the singleton LayoutDelegate instance.
+  static LayoutDelegate* Get();

[sky, 2016/11/15 17:43:38]

Thanks for the improved docs in GetActiveInstance. I still think having two
functions is error prone. It's all two easy to review code calling Get() and not
realize it's not the one that should be called. AFAICT Get() is only called from
GetActiveInstance(). In which case can Get() be removed and/or made private? I
would also rename GetActiveInstance() to Get().

[Elly Fong-Jones, 2016/11/15 19:47:26]

Done.

+
+  // Returns the active LayoutDelegate singleton, depending on UI configuration.
+  // By default, this is the same instance returned by Get(), but if Harmony
+  // or another UI style is enabled, this may be an instance of a LayoutDelegate
+  // subclass instead.
+  static LayoutDelegate* GetActiveInstance();
+
+  // Returns a layout distance, indexed by |type|. These distances are in
+  // device-independent units.
+  virtual int GetLayoutDistance(LayoutDistanceType type) const;
+
+  // Returns the alignment used for control labels in a GridLayout; for example,
+  // in this GridLayout:
+  //   ---------------------------
+  //   | Label 1      Checkbox 1 |
+  //   | Label 2      Checkbox 2 |
+  //   ---------------------------
+  // This value controls the alignment used for "Label 1" and "Label 2".
+  virtual views::GridLayout::Alignment GetControlLabelGridAlignment() const;
+
+  // Returns whether to use extra padding on dialogs. If this is false, content
+  // Views for dialogs should not insert extra padding at their own edges.
+  virtual bool UseExtraDialogPadding() const;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(LayoutDelegate);

[sky, 2016/11/15 17:43:38]

I think you want DISALLOW_IMPLICIT_CONSTRUCTORS.

[Elly Fong-Jones, 2016/11/15 19:47:26]

It has an explicitly-declared LayoutDelegate() above, though (which is needed
for LazyInstance to work, it seems).

+};
+
+#endif  // CHROME_BROWSER_UI_VIEWS_HARMONY_LAYOUT_DELEGATE_H_