Remove root window from screen_ash

ash/screen_ash.cc

Index: ash/screen_ash.cc
diff --git a/ash/screen_ash.cc b/ash/screen_ash.cc
index ed83c46d4501f1e2746cafe4d47d7bcd8e9f7612..c7d9cb94187e2fa0ade73b2f86f9204588cf84ac 100644
--- a/ash/screen_ash.cc
+++ b/ash/screen_ash.cc
@@ -21,8 +21,7 @@ aura::MonitorManager* GetMonitorManager() {
 }
 }  // namespace
 
-ScreenAsh::ScreenAsh(aura::RootWindow* root_window)
-    : root_window_(root_window) {
+ScreenAsh::ScreenAsh() {
 }
 
 ScreenAsh::~ScreenAsh() {
@@ -30,21 +29,29 @@ ScreenAsh::~ScreenAsh() {
 
 // static
 gfx::Rect ScreenAsh::GetMaximizedWindowBounds(aura::Window* window) {
-  return Shell::GetInstance()->shelf()->GetMaximizedWindowBounds(window);
+  if (window->GetRootWindow() == Shell::GetPrimaryRootWindow())
+    return Shell::GetInstance()->shelf()->GetMaximizedWindowBounds(window);
+  else
+    return gfx::Screen::GetMonitorNearestWindow(window).bounds();
 }
 
 // static
 gfx::Rect ScreenAsh::GetUnmaximizedWorkAreaBounds(aura::Window* window) {
-  return Shell::GetInstance()->shelf()->GetUnmaximizedWorkAreaBounds(window);
+  if (window->GetRootWindow() == Shell::GetPrimaryRootWindow())
+    return Shell::GetInstance()->shelf()->GetUnmaximizedWorkAreaBounds(window);
+  else
+    return gfx::Screen::GetMonitorNearestWindow(window).work_area();
 }
 
 gfx::Point ScreenAsh::GetCursorScreenPoint() {
-  return root_window_->last_mouse_location();
+  // TODO(oshima): Support multiple root window.
+  return Shell::GetPrimaryRootWindow()->last_mouse_location();
 }
 
 gfx::NativeWindow ScreenAsh::GetWindowAtCursorScreenPoint() {
   const gfx::Point point = gfx::Screen::GetCursorScreenPoint();
-  return root_window_->GetTopWindowContainingPoint(point);
+  // TODO(oshima): convert point to relateive to the root window.
+  return Shell::GetRootWindowAt(point)->GetTopWindowContainingPoint(point);
 }
 
 int ScreenAsh::GetNumMonitors() {