Make it possible to change the viewport size

mojo/services/window_manager/window_manager_app.cc

Index: mojo/services/window_manager/window_manager_app.cc
diff --git a/mojo/services/window_manager/window_manager_app.cc b/mojo/services/window_manager/window_manager_app.cc
index 9af766e194e5af9113563f086c65f74b4569fdc7..538bf7ecb25efe72d67b30f0b57a9e9017bcad88 100644
--- a/mojo/services/window_manager/window_manager_app.cc
+++ b/mojo/services/window_manager/window_manager_app.cc
@@ -365,6 +365,10 @@ void WindowManagerApp::Unregister(View* view) {
   view_id_to_window_map_.erase(it);
 }
 
+void WindowManagerApp::SetViewportSize(const gfx::Size& size) {
+  window_manager_client_->SetViewportSize(Size::From(size));
+}
+
 void WindowManagerApp::LaunchViewManager(ApplicationImpl* app) {
   // TODO(sky): figure out logic if this connection goes away.
   view_manager_client_factory_.reset(