Use overlay scrollbars for the cros system menu.

ash/common/system/tray/fixed_sized_scroll_view.cc

Index: ash/common/system/tray/fixed_sized_scroll_view.cc
diff --git a/ash/common/system/tray/fixed_sized_scroll_view.cc b/ash/common/system/tray/fixed_sized_scroll_view.cc
index f63f84bd008833b8038d6093a63a848e19da1c2c..4bc89220354cb76bb65108bd524b0fc8f2d64306 100644
--- a/ash/common/system/tray/fixed_sized_scroll_view.cc
+++ b/ash/common/system/tray/fixed_sized_scroll_view.cc
@@ -4,10 +4,24 @@
 
 #include "ash/common/system/tray/fixed_sized_scroll_view.h"
 
+#include "ash/common/material_design/material_design_controller.h"
+#include "ui/views/background.h"
+#include "ui/views/controls/scrollbar/overlay_scroll_bar.h"
+
 namespace ash {
 
+namespace {
+
+bool UseMd() {
+  return MaterialDesignController::IsSystemTrayMenuMaterial();
+}
+
+}  // namespace
+
 FixedSizedScrollView::FixedSizedScrollView() {
   set_notify_enter_exit_on_child(true);
+  if (UseMd())
+    SetVerticalScrollBar(new views::OverlayScrollBar(false));
 }
 
 FixedSizedScrollView::~FixedSizedScrollView() {}
@@ -18,12 +32,18 @@ void FixedSizedScrollView::SetContentsView(views::View* view) {
 }
 
 void FixedSizedScrollView::SetFixedSize(const gfx::Size& size) {
+  DCHECK(!UseMd());
   if (fixed_size_ == size)
     return;
   fixed_size_ = size;
   PreferredSizeChanged();
 }
 
+void FixedSizedScrollView::set_fixed_size(const gfx::Size& size) {
+  DCHECK(!UseMd());
+  fixed_size_ = size;
+}
+
 gfx::Size FixedSizedScrollView::GetPreferredSize() const {
   gfx::Size size =
       fixed_size_.IsEmpty() ? contents()->GetPreferredSize() : fixed_size_;
@@ -33,6 +53,11 @@ gfx::Size FixedSizedScrollView::GetPreferredSize() const {
 }
 
 void FixedSizedScrollView::Layout() {
+  if (UseMd()) {
+    views::ScrollView::Layout();
+    return;
+  }
+
   gfx::Rect bounds = gfx::Rect(contents()->GetPreferredSize());
   bounds.set_width(std::max(0, width() - GetScrollBarWidth()));
   // Keep the origin of the contents unchanged so that the list will not scroll
@@ -51,6 +76,9 @@ void FixedSizedScrollView::Layout() {
 }
 
 void FixedSizedScrollView::OnBoundsChanged(const gfx::Rect& previous_bounds) {
+  if (UseMd())
+    return;
+
   gfx::Rect bounds = gfx::Rect(contents()->GetPreferredSize());
   bounds.set_width(std::max(0, width() - GetScrollBarWidth()));
   contents()->SetBoundsRect(bounds);