Plumb ViewportMetrics change notifications around the world and back.

services/view_manager/test_server_view_delegate.cc

Index: services/view_manager/test_server_view_delegate.cc
diff --git a/services/view_manager/test_server_view_delegate.cc b/services/view_manager/test_server_view_delegate.cc
index cf01d171b9338ce09c7f9edcb202bcf72df16616..85fd66b1f2ce96ab326af225bf1ba37bde5338cf 100644
--- a/services/view_manager/test_server_view_delegate.cc
+++ b/services/view_manager/test_server_view_delegate.cc
@@ -34,6 +34,12 @@ void TestServerViewDelegate::OnViewBoundsChanged(const ServerView* view,
                                                  const gfx::Rect& new_bounds) {
 }
 
+void TestServerViewDelegate::OnViewViewportMetricsChanged(
+    const ServerView* view,
+    const mojo::ViewportMetrics& old_metrics,
+    const mojo::ViewportMetrics& new_metrics) {
+}
+
 void TestServerViewDelegate::OnViewSurfaceIdChanged(const ServerView* view) {
 }