Split surface id and simplify connecting to surfaces service

sky/viewer/document_view.cc

Index: sky/viewer/document_view.cc
diff --git a/sky/viewer/document_view.cc b/sky/viewer/document_view.cc
index 722a935ebe915a0fe9b56cf0a6e8cd72641ef39e..47ab3e3540e1815ccd4885ad32c60d1d0f8266ab 100644
--- a/sky/viewer/document_view.cc
+++ b/sky/viewer/document_view.cc
@@ -156,7 +156,8 @@ void DocumentView::BeginFrame(base::TimeTicks frame_time) {
 }
 
 void DocumentView::OnSurfaceIdAvailable(mojo::SurfaceIdPtr surface_id) {
-  root_->SetSurfaceId(surface_id.Pass());
+  if (root_)

[jamesr, 2014/12/16 00:02:47]

this is not directly related, but fixes a flaky shutdown crash

[esprehn, 2014/12/16 00:51:11]

Wouldn't we want to shutdown the connection to surfaces service after
OnViewDestroyed instead? What frees the surface with this id?

[jamesr, 2014/12/16 00:56:09]

This isn't about controlling the surface, this is about communicating the ID
with the view manager.  At this point, if root_ is null then our app's part of
the view manager lib (including its connection to the view manager service) have
already gone down so there's nowhere to send the ID.

The surface itself is managed elsewhere.

[esprehn, 2014/12/16 01:23:57]

Why do we even get this message if everything is torn down?

+    root_->SetSurfaceId(surface_id.Pass());
 }
 
 void DocumentView::PaintContents(SkCanvas* canvas, const gfx::Rect& clip) {