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

ui/views/layout/box_layout_unittest.cc

Index: ui/views/layout/box_layout_unittest.cc
diff --git a/ui/views/layout/box_layout_unittest.cc b/ui/views/layout/box_layout_unittest.cc
index dcf3227070e2e16bca2499e68a4941f5b504579b..2f6bf8ac1647ac8f9e4309deedd629da4cf8ad60 100644
--- a/ui/views/layout/box_layout_unittest.cc
+++ b/ui/views/layout/box_layout_unittest.cc
@@ -109,3 +109,20 @@ TEST_F(BoxLayoutTest, InvisibleChild) {
   layout_->Layout(host_.get());
   EXPECT_EQ(gfx::Rect(10, 10, 10, 10), v2->bounds());
 }
+
+TEST_F(BoxLayoutTest, DistributeEmptySpace) {
+  layout_.reset(
+      new views::BoxLayout(views::BoxLayout::kHorizontal, 10, 10, 10));
+  layout_->set_spread_blank_space(true);
+
+  views::View* v1 = new StaticSizedView(gfx::Size(20, 20));
+  host_->AddChildView(v1);
+  views::View* v2 = new StaticSizedView(gfx::Size(10, 10));
+  host_->AddChildView(v2);
+  EXPECT_EQ(gfx::Size(60, 40), layout_->GetPreferredSize(host_.get()));
+
+  host_->SetBounds(0, 0, 100, 40);
+  layout_->Layout(host_.get());
+  EXPECT_EQ(gfx::Rect(10, 10, 40, 20).ToString(), v1->bounds().ToString());
+  EXPECT_EQ(gfx::Rect(60, 10, 30, 20).ToString(), v2->bounds().ToString());
+}