Add views::View::set_preferred_size, use it in a few places.

ui/views/view.h

 // Copyright (c) 2012 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_VIEW_H_
 #define UI_VIEWS_VIEW_H_
 
 #include <stddef.h>
 
 #include <algorithm>
@@ skipping 255 matching lines @@
   gfx::Rect GetVisibleBounds() const;
 
   // Return the bounds of the View in screen coordinate system.
   gfx::Rect GetBoundsInScreen() const;
 
   // Returns the baseline of this view, or -1 if this view has no baseline. The
   // return value is relative to the preferred height.
   virtual int GetBaseline() const;
 
   // Get the size the View would like to be, if enough space were available.
+  // First checks |preferred_size_|, then |layout_manager_|, then
+  // CalculatePreferredSize().
+  // TODO(estade): migrate existing GetPreferredSize() overrides to
+  // CalculatePreferredSize() and make this function non-virtual.
   virtual gfx::Size GetPreferredSize() const;
 
+  // Sets the size that this View will request during layout. The actual size
+  // may differ.

[sky, 2017/05/15 21:56:16]

Please also add a comment that in very rare cases should you need to explicitly
set this.

[Evan Stade, 2017/05/15 22:04:04]

Done.

+  void set_preferred_size(const gfx::Size& size) { preferred_size_ = size; }
+
   // Convenience method that sizes this view to its preferred size.
   void SizeToPreferredSize();
 
   // Gets the minimum size of the view. View's implementation invokes
   // GetPreferredSize.
   virtual gfx::Size GetMinimumSize() const;
 
   // Gets the maximum size of the view. Currently only used for sizing shell
   // windows.
   virtual gfx::Size GetMaximumSize() const;
@@ skipping 760 matching lines @@
 
     // Whether the press may generate a drag.
     bool possible_drag;
 
     // Coordinates of the mouse press.
     gfx::Point start_pt;
   };
 
   // Size and disposition ------------------------------------------------------
 
+  // Calculates the natural size for the View, to be taken into consideration
+  // when the parent is performing layout.
+  virtual gfx::Size CalculatePreferredSize() const;
+
   // Override to be notified when the bounds of the view have changed.
   virtual void OnBoundsChanged(const gfx::Rect& previous_bounds);
 
   // Called when the preferred size of a child view changed.  This gives the
   // parent an opportunity to do a fresh layout if that makes sense.
   virtual void ChildPreferredSizeChanged(View* child) {}
 
   // Called when the visibility of a child view changed.  This gives the parent
   // an opportunity to do a fresh layout if that makes sense.
   virtual void ChildVisibilityChanged(View* child) {}
@@ skipping 497 matching lines @@
 #if DCHECK_IS_ON()
   // True while iterating over |children_|. Used to detect and DCHECK when
   // |children_| is mutated during iteration.
   mutable bool iterating_;
 #endif
 
   bool can_process_events_within_subtree_;
 
   // Size and disposition ------------------------------------------------------
 
+  base::Optional<gfx::Size> preferred_size_;
+
   // This View's bounds in the parent coordinate system.
   gfx::Rect bounds_;
 
   // Whether this view is visible.
   bool visible_;
 
   // Whether this view is enabled.
   bool enabled_;
 
   // When this flag is on, a View receives a mouse-enter and mouse-leave event
@@ skipping 108 matching lines @@
   // Observers -------------------------------------------------------------
 
   base::ObserverList<ViewObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(View);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_VIEW_H_