Allow platform apps to specify a maximum size for the shell container.

ui/views/widget/widget.cc

Index: ui/views/widget/widget.cc
diff --git a/ui/views/widget/widget.cc b/ui/views/widget/widget.cc
index 6073a89e71d7f460037f9afd976da9951d0db700..6a2fdc92d7f8985df381bfe907f78f3f19655ee4 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -968,6 +968,10 @@ gfx::Size Widget::GetMinimumSize() {
   return non_client_view_ ? non_client_view_->GetMinimumSize() : gfx::Size();
 }
 
+gfx::Size Widget::GetMaximumSize() {
+  return non_client_view_ ? non_client_view_->GetMaximumSize() : gfx::Size();
+}
+
 void Widget::OnNativeWidgetSizeChanged(const gfx::Size& new_size) {
   root_view_->SetSize(new_size);