Changes how window is updated when display changes in mash

ui/display/display_list.cc

 // Copyright 2016 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 "ui/display/display_list.h"
 
 #include "base/memory/ptr_util.h"
 #include "ui/display/display_observer.h"
 
 namespace display {
@@ skipping 34 matching lines @@
     const {
   return primary_display_index_ == -1
              ? displays_.end()
              : displays_.begin() + primary_display_index_;
 }
 
 std::unique_ptr<DisplayListObserverLock> DisplayList::SuspendObserverUpdates() {
   return base::WrapUnique(new DisplayListObserverLock(this));
 }
 
-void DisplayList::UpdateDisplay(const Display& display) {
-  UpdateDisplay(display, GetTypeByDisplayId(display.id()));
+uint32_t DisplayList::UpdateDisplay(const Display& display) {
+  return UpdateDisplay(display, GetTypeByDisplayId(display.id()));
 }
 
-void DisplayList::UpdateDisplay(const Display& display, Type type) {
+uint32_t DisplayList::UpdateDisplay(const Display& display, Type type) {
   auto iter = FindDisplayByIdInternal(display.id());
   DCHECK(iter != displays_.end());
 
   Display* local_display = &(*iter);
   uint32_t changed_values = 0;
   if (type == Type::PRIMARY &&
       static_cast<int>(iter - displays_.begin()) !=
           static_cast<int>(GetPrimaryDisplayIterator() - displays_.begin())) {
     primary_display_index_ = static_cast<int>(iter - displays_.begin());
     // ash::DisplayManager only notifies for the Display gaining primary, not
@@ skipping 13 matching lines @@
     changed_values |= DisplayObserver::DISPLAY_METRIC_ROTATION;
   }
   if (local_display->device_scale_factor() != display.device_scale_factor()) {
     local_display->set_device_scale_factor(display.device_scale_factor());
     changed_values |= DisplayObserver::DISPLAY_METRIC_DEVICE_SCALE_FACTOR;
   }
   if (should_notify_observers()) {
     for (DisplayObserver& observer : observers_)
       observer.OnDisplayMetricsChanged(*local_display, changed_values);
   }
+  return changed_values;
 }
 
 void DisplayList::AddDisplay(const Display& display, Type type) {
   DCHECK(displays_.end() == FindDisplayByIdInternal(display.id()));
   displays_.push_back(display);
   if (type == Type::PRIMARY)
     primary_display_index_ = static_cast<int>(displays_.size()) - 1;
   if (should_notify_observers()) {
     for (DisplayObserver& observer : observers_)
       observer.OnDisplayAdded(display);
@@ skipping 40 matching lines @@
 DisplayList::Displays::iterator DisplayList::FindDisplayByIdInternal(
     int64_t id) {
   for (auto iter = displays_.begin(); iter != displays_.end(); ++iter) {
     if (iter->id() == id)
       return iter;
   }
   return displays_.end();
 }
 
 }  // namespace display