Plumb ViewportMetrics change notifications around the world and back.

services/view_manager/test_server_view_delegate.h

Index: services/view_manager/test_server_view_delegate.h
diff --git a/services/view_manager/test_server_view_delegate.h b/services/view_manager/test_server_view_delegate.h
index 82f0d83796657c9cdd3222bdaa64e8c7bcb62a9f..dd4e0dc680a4af816e26d594c871c0d7b575c7bb 100644
--- a/services/view_manager/test_server_view_delegate.h
+++ b/services/view_manager/test_server_view_delegate.h
@@ -28,6 +28,10 @@ class TestServerViewDelegate : public ServerViewDelegate {
   void OnViewBoundsChanged(const ServerView* view,
                            const gfx::Rect& old_bounds,
                            const gfx::Rect& new_bounds) override;
+  void OnViewViewportMetricsChanged(
+      const ServerView* view,
+      const mojo::ViewportMetrics& old_metrics,
+      const mojo::ViewportMetrics& new_metrics) override;
   void OnViewSurfaceIdChanged(const ServerView* view) override;
   void OnViewReordered(const ServerView* view,
                        const ServerView* relative,