Remove manual layout for ScrollableView

The manual layout just put one child view at the start and one in the
middle vertically. This CL removes the manual layout by introducing two
container views to be placed in equal size vertically.

BUG=1005568

Change-Id: Iae552da751d71175d3967deaf788a323221d0a1c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1884999
Commit-Queue: Wei Li <weili@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710578}

ui/views/examples/scroll_view_example.cc

@@ -14,6 +14,7 @@
 #include "ui/views/background.h"
 #include "ui/views/controls/button/label_button.h"
 #include "ui/views/controls/button/radio_button.h"
+#include "ui/views/layout/box_layout.h"
 #include "ui/views/layout/grid_layout.h"
 #include "ui/views/view.h"
 
@@ -28,8 +29,19 @@ class ScrollViewExample::ScrollableView : public View {
  public:
   ScrollableView() {
     SetColor(SK_ColorRED, SK_ColorCYAN);
-    AddChildView(new LabelButton(nullptr, ASCIIToUTF16("Button")));
-    AddChildView(new RadioButton(ASCIIToUTF16("Radio Button"), 0));
+
+    auto* layout_manager = SetLayoutManager(std::make_unique<views::BoxLayout>(
+        views::BoxLayout::Orientation::kVertical, gfx::Insets(), 0));
+
+    const auto add_child = [this](std::unique_ptr<View> view) {
+      auto* container = AddChildView(std::make_unique<View>());
+      container->SetLayoutManager(std::make_unique<views::BoxLayout>(
+          views::BoxLayout::Orientation::kVertical));
+      container->AddChildView(std::move(view));
+    };
+    add_child(std::make_unique<LabelButton>(nullptr, ASCIIToUTF16("Button")));
+    add_child(std::make_unique<RadioButton>(ASCIIToUTF16("Radio Button"), 0));
+    layout_manager->SetDefaultFlex(1);
   }
 
   void SetColor(SkColor from, SkColor to) {
@@ -37,19 +49,6 @@ class ScrollViewExample::ScrollableView : public View {
     to_color_ = to;
   }
 
-  void PlaceChildY(size_t index, int y) {
-    View* view = children()[index];
-    gfx::Size size = view->GetPreferredSize();
-    view->SetBounds(0, y, size.width(), size.height());
-  }
-
-  // View
-  void Layout() override {
-    PlaceChildY(0, 0);
-    PlaceChildY(1, height() / 2);
-    SizeToPreferredSize();
-  }
-
   void OnPaintBackground(gfx::Canvas* canvas) override {
     cc::PaintFlags flags;
     flags.setShader(gfx::CreateGradientShader(
@@ -58,10 +57,6 @@ class ScrollViewExample::ScrollableView : public View {
     canvas->DrawRect(GetLocalBounds(), flags);
   }
 
-  gfx::Size CalculatePreferredSize() const override {
-    return gfx::Size(width(), height());
-  }
-
  private:
   SkColor from_color_;
   SkColor to_color_;