views: Add option in BoxLayout to spread blank space among the child views.

ui/views/layout/box_layout.h

Index: ui/views/layout/box_layout.h
diff --git a/ui/views/layout/box_layout.h b/ui/views/layout/box_layout.h
index 723511978e3e7991817cc645fe1563881b920ef4..cc23c71d2ce36134d0c26bfd91c63df32cfe77f0 100644
--- a/ui/views/layout/box_layout.h
+++ b/ui/views/layout/box_layout.h
@@ -40,6 +40,10 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
             int between_child_spacing);
   virtual ~BoxLayout();
 
+  void set_spread_blank_space(bool spread) {
+    spread_blank_space_ = spread;
+  }
+
   // Overridden from views::LayoutManager:
   virtual void Layout(View* host) OVERRIDE;
   virtual gfx::Size GetPreferredSize(View* host) OVERRIDE;
@@ -54,6 +58,10 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
   // Spacing to put in between child views.
   const int between_child_spacing_;
 
+  // Whether the available extra space should be distributed among the child
+  // views.
+  bool spread_blank_space_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(BoxLayout);
 };