exo: Initial support for multiple displays in ARC

components/exo/wm_helper_ash.cc

Index: components/exo/wm_helper_ash.cc
diff --git a/components/exo/wm_helper_ash.cc b/components/exo/wm_helper_ash.cc
index 413eeb8e6a60302aea0b24eba02c7a5bdcc878e1..37d38c5640b54668f08e6cd48a85b2fecca18376 100644
--- a/components/exo/wm_helper_ash.cc
+++ b/components/exo/wm_helper_ash.cc
@@ -23,6 +23,7 @@ namespace exo {
 WMHelperAsh::WMHelperAsh() {
   ash::WmShell::Get()->AddShellObserver(this);
   ash::Shell::GetInstance()->activation_client()->AddObserver(this);
+  ash::Shell::GetInstance()->window_tree_host_manager()->AddObserver(this);
   aura::client::FocusClient* focus_client =
       aura::client::GetFocusClient(ash::Shell::GetPrimaryRootWindow());
   focus_client->AddObserver(this);
@@ -37,6 +38,7 @@ WMHelperAsh::~WMHelperAsh() {
       aura::client::GetFocusClient(ash::Shell::GetPrimaryRootWindow());
   focus_client->RemoveObserver(this);
   ash::Shell::GetInstance()->activation_client()->RemoveObserver(this);
+  ash::Shell::GetInstance()->window_tree_host_manager()->RemoveObserver(this);
   ash::WmShell::Get()->RemoveShellObserver(this);
   ui::DeviceDataManager::GetInstance()->RemoveObserver(this);
   ash::WmShell::Get()->system_tray_notifier()->RemoveAccessibilityObserver(
@@ -144,6 +146,10 @@ void WMHelperAsh::OnMaximizeModeEnded() {
   NotifyMaximizeModeEnded();
 }
 
+void WMHelperAsh::OnDisplayConfigurationChanged() {
+  NotifyDisplayConfigurationChanged();
+}
+
 void WMHelperAsh::OnKeyboardDeviceConfigurationChanged() {
   NotifyKeyboardDeviceConfigurationChanged();
 }