Add main axis alignment for BoxLayout.

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 7670d8cb05e7bd15b59771b2e95c3ade65aabf84..ce2cbd5c9378516259107e156c50fd5c69b19030 100644
--- a/ui/views/layout/box_layout.h
+++ b/ui/views/layout/box_layout.h
@@ -11,6 +11,7 @@
 #include "ui/views/layout/layout_manager.h"
 
 namespace gfx {
+class Rect;
 class Size;
 }
 
@@ -30,6 +31,16 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
     kVertical,
   };
 
+  enum BoxPack {
+    BOX_PACK_START,
+    BOX_PACK_CENTER,
+    BOX_PACK_END,
+    // TODO(calamity): Add BOX_PACK_JUSTIFY which spreads blank space in-
+    // between the child views.
+  };
+
+  // TODO(calamity): Add BoxAlign property to allow cross axis alignment.
+
   // Use |inside_border_horizontal_spacing| and
   // |inside_border_vertical_spacing| to add additional space between the child
   // view area and the host view border. |between_child_spacing| controls the
@@ -44,12 +55,19 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
     spread_blank_space_ = spread;
   }
 
+  void set_box_pack(BoxPack box_pack) { box_pack_ = box_pack; }
+
   // Overridden from views::LayoutManager:
   virtual void Layout(View* host) OVERRIDE;
   virtual gfx::Size GetPreferredSize(View* host) OVERRIDE;
   virtual int GetPreferredHeightForWidth(View* host, int width) OVERRIDE;
 
  private:
+  int MainAxisSize(const gfx::Rect& child_area);
+  int MainAxisPosition(const gfx::Rect& child_area);
+  void SetMainAxisSize(gfx::Rect* child_area, int size);
+  void SetMainAxisPosition(gfx::Rect* child_area, int position);
+
   // The preferred size for the dialog given the width of the child area.
   gfx::Size GetPreferredSizeForChildWidth(View* host, int child_area_width);
 
@@ -66,9 +84,14 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
   const int between_child_spacing_;
 
   // Whether the available extra space should be distributed among the child
-  // views.
+  // views. This increases the size of child views rather than the space
+  // between them.
   bool spread_blank_space_;
 
+  // The alignment of children in the main axis. This is BOX_PACK_START by
+  // default.
+  BoxPack box_pack_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(BoxLayout);
 };