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

ui/views/view.h

Index: ui/views/view.h
diff --git a/ui/views/view.h b/ui/views/view.h
index d1f69707fda4a74ca022439077464b8205df2fb0..117c1ab5dd03c4adcc897204d9cfa38062b0c68e 100644
--- a/ui/views/view.h
+++ b/ui/views/view.h
@@ -273,8 +273,16 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
   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();
 
@@ -1055,6 +1063,10 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
 
   // 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);
 
@@ -1572,6 +1584,8 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
 
   // Size and disposition ------------------------------------------------------
 
+  base::Optional<gfx::Size> preferred_size_;
+
   // This View's bounds in the parent coordinate system.
   gfx::Rect bounds_;