Use LayoutManager for OverlayScrollBar.

As with ScrollBarViews, this can just size the thumb extra-large and rely on
ScrollBar::Update() to do the real sizing.  To facilitate this, override
GetInsets() to convert GetContentsBounds() into the same thing as
GetTrackBounds(), then use a FillLayout.

Also reorders functions to match superclass order and access level.

Bug: 1005568
Change-Id: Iad7fed5501adcf301ac66f9390c2545a6e00c827
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1824028
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699584}

ui/views/controls/scrollbar/overlay_scroll_bar.cc

@@ -13,6 +13,7 @@
 #include "ui/native_theme/overlay_scrollbar_constants_aura.h"
 #include "ui/views/background.h"
 #include "ui/views/border.h"
+#include "ui/views/layout/fill_layout.h"
 
 namespace views {
 namespace {
@@ -125,52 +126,45 @@ void OverlayScrollBar::Thumb::OnStateChanged() {
 }
 
 OverlayScrollBar::OverlayScrollBar(bool horizontal) : ScrollBar(horizontal) {
-  auto* thumb = new Thumb(this);
-  SetThumb(thumb);
-  thumb->Init();
   set_notify_enter_exit_on_child(true);
   SetPaintToLayer();
   layer()->SetMasksToBounds(true);
   layer()->SetFillsBoundsOpaquely(false);
+
+  // Allow the thumb to take up the whole size of the scrollbar.  Layout need
+  // only set the thumb cross-axis coordinate; ScrollBar::Update() will set the
+  // thumb size/offset.
+  SetLayoutManager(std::make_unique<views::FillLayout>());
+  auto* thumb = new Thumb(this);
+  SetThumb(thumb);
+  thumb->Init();
 }
 
 OverlayScrollBar::~OverlayScrollBar() = default;
 
-gfx::Rect OverlayScrollBar::GetTrackBounds() const {
-  gfx::Rect local = GetLocalBounds();
-  // The track has to be wide enough for the thumb.
-  local.Inset(gfx::Insets(IsHorizontal() ? -kThumbHoverOffset : 0,
-                          IsHorizontal() ? 0 : -kThumbHoverOffset, 0, 0));
-  return local;
+gfx::Insets OverlayScrollBar::GetInsets() const {
+  return IsHorizontal() ? gfx::Insets(-kThumbHoverOffset, 0, 0, 0)
+                        : gfx::Insets(0, -kThumbHoverOffset, 0, 0);
 }
 
-int OverlayScrollBar::GetThickness() const {
-  return kThumbThickness;
+void OverlayScrollBar::OnMouseEntered(const ui::MouseEvent& event) {
+  Show();
 }
 
-bool OverlayScrollBar::OverlapsContent() const {
-  return true;
+void OverlayScrollBar::OnMouseExited(const ui::MouseEvent& event) {
+  StartHideCountdown();
 }
 
-void OverlayScrollBar::Layout() {
-  gfx::Rect thumb_bounds = GetTrackBounds();
-  BaseScrollBarThumb* thumb = GetThumb();
-  if (IsHorizontal()) {
-    thumb_bounds.set_x(thumb->x());
-    thumb_bounds.set_width(thumb->width());
-  } else {
-    thumb_bounds.set_y(thumb->y());
-    thumb_bounds.set_height(thumb->height());
-  }
-  thumb->SetBoundsRect(thumb_bounds);
+bool OverlayScrollBar::OverlapsContent() const {
+  return true;
 }
 
-void OverlayScrollBar::OnMouseEntered(const ui::MouseEvent& event) {
-  Show();
+gfx::Rect OverlayScrollBar::GetTrackBounds() const {
+  return GetContentsBounds();
 }
 
-void OverlayScrollBar::OnMouseExited(const ui::MouseEvent& event) {
-  StartHideCountdown();
+int OverlayScrollBar::GetThickness() const {
+  return kThumbThickness;
 }
 
 void OverlayScrollBar::Show() {

ui/views/controls/scrollbar/overlay_scroll_bar.h

@@ -20,18 +20,13 @@ class VIEWS_EXPORT OverlayScrollBar : public ScrollBar {
   explicit OverlayScrollBar(bool horizontal);
   ~OverlayScrollBar() override;
 
- protected:
-  // ScrollBar overrides:
-  gfx::Rect GetTrackBounds() const override;
-
-  // ScrollBar overrides:
-  int GetThickness() const override;
-  bool OverlapsContent() const override;
-
-  // View overrides:
-  void Layout() override;
+  // ScrollBar:
+  gfx::Insets GetInsets() const override;
   void OnMouseEntered(const ui::MouseEvent& event) override;
   void OnMouseExited(const ui::MouseEvent& event) override;
+  bool OverlapsContent() const override;
+  gfx::Rect GetTrackBounds() const override;
+  int GetThickness() const override;
 
  private:
   class Thumb : public BaseScrollBarThumb {