views: add layout delegates

ui/views/layout/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 UI_VIEWS_LAYOUT_LAYOUT_DELEGATE_H_
+#define UI_VIEWS_LAYOUT_LAYOUT_DELEGATE_H_
+
+#include "ui/views/layout/grid_layout.h"
+
+namespace views {
+
+class VIEWS_EXPORT LayoutDelegate {

[sky, 2016/11/08 23:34:00]

Layout spacing and alignment are best left to clients, and not in views itself.
From this patch you need two things from this class:

. GridLayout::CreatePanel. In hind site this shouldn't exist in views, it should
move to client code, probably harmony in this patch.

. The insets and padding for DialogClientView. I would rather there is explicit
functions on ViewsDelegate to get what you need. You can make these functions
take in a View for context (if needed). If you envision needing a bunch of
things, then I'm ok with a LayoutConstants class that is obtained from
ViewsDelegate.

+ public:
+  enum 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,
+  };
+
+  // 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 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;
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_LAYOUT_LAYOUT_DELEGATE_H_