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

ui/views/layout/box_layout.cc

Index: ui/views/layout/box_layout.cc
diff --git a/ui/views/layout/box_layout.cc b/ui/views/layout/box_layout.cc
index 7282431685715c1efd8f510b1dd057821b73b590..4db0677141d08e66ecee35386c7b6b8aebbcf65f 100644
--- a/ui/views/layout/box_layout.cc
+++ b/ui/views/layout/box_layout.cc
@@ -17,7 +17,8 @@ BoxLayout::BoxLayout(BoxLayout::Orientation orientation,
     : orientation_(orientation),
       inside_border_horizontal_spacing_(inside_border_horizontal_spacing),
       inside_border_vertical_spacing_(inside_border_vertical_spacing),
-      between_child_spacing_(between_child_spacing) {
+      between_child_spacing_(between_child_spacing),
+      spread_blank_space_(false) {
 }
 
 BoxLayout::~BoxLayout() {
@@ -30,17 +31,45 @@ void BoxLayout::Layout(View* host) {
                    inside_border_vertical_spacing_);
   int x = child_area.x();
   int y = child_area.y();
+
+  int padding = 0;
+  if (spread_blank_space_) {
+    int total = 0;
+    int visible = 0;
+    for (int i = 0; i < host->child_count(); ++i) {
+      View* child = host->child_at(i);
+      if (!child->visible())
+        continue;
+      if (orientation_ == kHorizontal)
+        total += child->GetPreferredSize().width() + between_child_spacing_;
+      else
+        total += child->GetPreferredSize().height() + between_child_spacing_;
+      ++visible;
+    }
+
+    if (visible) {
+      total -= between_child_spacing_;
+      if (orientation_ == kHorizontal)
+        padding = (child_area.width() - total) / visible;
+      else
+        padding = (child_area.height() - total) / visible;
+
+      if (padding < 0)
+        padding = 0;
+    }
+  }
+
   for (int i = 0; i < host->child_count(); ++i) {
     View* child = host->child_at(i);
     if (child->visible()) {
       gfx::Rect bounds(x, y, child_area.width(), child_area.height());
       gfx::Size size(child->GetPreferredSize());
       if (orientation_ == kHorizontal) {
-        bounds.set_width(size.width());
-        x += size.width() + between_child_spacing_;
+        bounds.set_width(size.width() + padding);
+        x += size.width() + between_child_spacing_ + padding;
       } else {
-        bounds.set_height(size.height());
-        y += size.height() + between_child_spacing_;
+        bounds.set_height(size.height() + padding);
+        y += size.height() + between_child_spacing_ + padding;
       }
       // Clamp child view bounds to |child_area|.
       child->SetBoundsRect(bounds.Intersect(child_area));