BoxLayout: Added set_collapse_when_hidden(), like views::Label.

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 10f82b9aa544e349b18a852a4afe330de9176427..b962bc6471b27719474b39661c8e65aba8da3bf3 100644
--- a/ui/views/layout/box_layout.cc
+++ b/ui/views/layout/box_layout.cc
@@ -23,6 +23,7 @@ BoxLayout::BoxLayout(BoxLayout::Orientation orientation,
       cross_axis_alignment_(CROSS_AXIS_ALIGNMENT_STRETCH),
       default_flex_(0),
       minimum_cross_axis_size_(0),
+      collapse_when_hidden_(false),
       host_(NULL) {
 }
 
@@ -156,6 +157,9 @@ void BoxLayout::Layout(View* host) {
 
 gfx::Size BoxLayout::GetPreferredSize(const View* host) const {
   DCHECK_EQ(host_, host);
+  if (!host->visible() && collapse_when_hidden_)
+    return gfx::Size();
+
   // Calculate the child views' preferred width.
   int width = 0;
   if (orientation_ == kVertical) {