Adds capture to the mojo window_manager.

mojo/services/view_manager/public/cpp/lib/view.cc

Index: mojo/services/view_manager/public/cpp/lib/view.cc
diff --git a/mojo/services/view_manager/public/cpp/lib/view.cc b/mojo/services/view_manager/public/cpp/lib/view.cc
index ee645055bd5f4db2e665a1e5f367aa55e9aa7534..6e82802d08d323afd35a3c14d9b249bcd8b65a1f 100644
--- a/mojo/services/view_manager/public/cpp/lib/view.cc
+++ b/mojo/services/view_manager/public/cpp/lib/view.cc
@@ -273,6 +273,13 @@ void View::RemoveObserver(ViewObserver* observer) {
   observers_.RemoveObserver(observer);
 }
 
+View* View::GetRoot() {
+  View* root = this;
+  for (View* parent = this; parent; parent = parent->parent())
+    root = parent;
+  return root;
+}
+
 const View* View::GetRoot() const {
   const View* root = this;
   for (const View* parent = this; parent; parent = parent->parent())