Don't reset scroll position of contents on every ScrollView layout.

ash/common/system/chromeos/bluetooth/tray_bluetooth.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/common/system/chromeos/bluetooth/tray_bluetooth.h"
 
 #include "ash/common/material_design/material_design_controller.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/system/tray/fixed_sized_scroll_view.h"
 #include "ash/common/system/tray/hover_highlight_view.h"
@@ skipping 311 matching lines @@
     // Show user Bluetooth state if there is no bluetooth devices in list.
     if (device_map_.size() == 0) {
       if (bluetooth_available && bluetooth_enabled) {
         AddScrollListItem(l10n_util::GetStringUTF16(
                               IDS_ASH_STATUS_TRAY_BLUETOOTH_DISCOVERING),
                           false /* highlight */, false /* checked */,
                           true /* enabled */);
       }
     }
 
-    scroll_content()->SizeToPreferredSize();
+    scroll_content()->InvalidateLayout();
   }
 
   void AppendSameTypeDevicesToScrollList(const BluetoothDeviceList& list,
                                          bool highlight,
                                          bool checked,
                                          bool enabled) {
     for (size_t i = 0; i < list.size(); ++i) {
       HoverHighlightView* container = nullptr;
       if (UseMd()) {
         gfx::ImageSkia icon_image = CreateVectorIcon(
@@ skipping 385 matching lines @@
     detailed_->Update();
 }
 
 void TrayBluetooth::OnBluetoothDiscoveringChanged() {
   if (!detailed_)
     return;
   detailed_->Update();
 }
 
 }  // namespace ash