exo: Confine windows to primary display

Multi-display support in ARC was punted to the next milestone. This CL
temporarily prevents windows from being dragged to secondary displays
by using display rather than screen coordinates for window bounds.

BUG=714832
TEST=ARC apps cannot be dragged to secondary displays.

Review-Url: https://codereview.chromium.org/2860863004
Cr-Commit-Position: refs/heads/master@{#469514}

components/exo/shell_surface.cc

@@ -1532,7 +1532,9 @@ void ShellSurface::UpdateWidgetBounds() {
   const gfx::Rect widget_bounds = widget_->GetWindowBoundsInScreen();
   if (widget_bounds != new_widget_bounds) {
     if (bounds_mode_ != BoundsMode::CLIENT || !resizer_) {
-      widget_->SetBounds(new_widget_bounds);
+      // TODO(domlaskowski): Use screen coordinates once multi-display support
+      // lands in ARC. See crbug.com/718627.
+      widget_->GetNativeWindow()->SetBounds(new_widget_bounds);
       UpdateSurfaceBounds();
     } else {
       // TODO(domlaskowski): Synchronize window state transitions with the

components/exo/wm_helper_ash.cc

@@ -60,7 +60,9 @@ const display::ManagedDisplayInfo WMHelperAsh::GetDisplayInfo(
 }
 
 aura::Window* WMHelperAsh::GetContainer(int container_id) {
-  return ash::Shell::GetContainer(ash::Shell::GetRootWindowForNewWindows(),
+  // TODO(domlaskowski): Use target root window once multi-display support lands
+  // in ARC. See crbug.com/718627.
+  return ash::Shell::GetContainer(ash::Shell::GetPrimaryRootWindow(),
                                   container_id);
 }