aura: Add RootWindowObserver::OnKeyboardMappingChanged().

ui/aura/root_window.cc

Index: ui/aura/root_window.cc
diff --git a/ui/aura/root_window.cc b/ui/aura/root_window.cc
index 05b5124c63330f900c288cc465039f53aec67467..5dc7f60b1f54383173bd702a2c3e026bc604b5da 100644
--- a/ui/aura/root_window.cc
+++ b/ui/aura/root_window.cc
@@ -355,6 +355,11 @@ void RootWindow::OnWindowTransformed(Window* window, bool contained_mouse) {
   }
 }
 
+void RootWindow::OnKeyboardMappingChanged() {
+  FOR_EACH_OBSERVER(RootWindowObserver, observers_,
+                    OnKeyboardMappingChanged(this));
+}
+
 void RootWindow::AddRootWindowObserver(RootWindowObserver* observer) {
   observers_.AddObserver(observer);
 }