Plumb ViewportMetrics change notifications around the world and back.

mojo/services/view_manager/public/interfaces/view_manager.mojom

Index: mojo/services/view_manager/public/interfaces/view_manager.mojom
diff --git a/mojo/services/view_manager/public/interfaces/view_manager.mojom b/mojo/services/view_manager/public/interfaces/view_manager.mojom
index 55552f8cb06e8e2e799045ed2b98823a17db1448..2bdf1538f785901887e5f6748d2880753eb72863 100644
--- a/mojo/services/view_manager/public/interfaces/view_manager.mojom
+++ b/mojo/services/view_manager/public/interfaces/view_manager.mojom
@@ -159,6 +159,11 @@ interface ViewManagerClient {
                       mojo.Rect old_bounds,
                       mojo.Rect new_bounds);
 
+  // Invoked when the viewport metrics for the view have changed.

[sky, 2015/01/27 23:40:23]

Document this is only sent for the root. It's assumed the client will propagate
as necessary.

+  OnViewViewportMetricsChanged(uint32 view,
+                           mojo.ViewportMetrics old_metrics,

[sky, 2015/01/27 23:40:23]

nit: indent

+                           mojo.ViewportMetrics new_metrics);
+
   // Invoked when a change is done to the hierarchy. A value of 0 is used to
   // identify a null view. For example, if the old_parent is NULL, 0 is
   // supplied.
@@ -173,7 +178,7 @@ interface ViewManagerClient {
   // Invoked when the order of views within a parent changes.
   OnViewReordered(uint32 view_id,
                   uint32 relative_view_id,
-                  OrderDirection direction);                     
+                  OrderDirection direction);
 
   // Invoked when a view is deleted.
   OnViewDeleted(uint32 view);