exo: Make sure vsync observer is removed when Surface is destroyed.

components/exo/surface.cc

Index: components/exo/surface.cc
diff --git a/components/exo/surface.cc b/components/exo/surface.cc
index cbd8cf387c83bd49e6d94d5a6ae0b9f2d0a85a35..dffcaee6487592251ba2233159b312b3e5792e16 100644
--- a/components/exo/surface.cc
+++ b/components/exo/surface.cc
@@ -205,6 +205,8 @@ Surface::~Surface() {
     observer.OnSurfaceDestroying(this);
 
   window_->RemoveObserver(this);
+  if (window_->layer()->GetCompositor())
+    window_->layer()->GetCompositor()->vsync_manager()->RemoveObserver(this);

[Fady Samuel, 2017/01/11 20:33:04]

drive-by question: What does exo use the vsync manager for? It should be using
BeginFrames instead?

[reveman, 2017/01/11 21:52:08]

We use it to implement the presentation time protocol
(https://cs.chromium.org/chromium/src/third_party/wayland-protocols/src/stable...).
It provides clients with presentation timing feedback. The motion event wayland
perftest client is using this to accurately measure end-to-end latency and arc++
will use this in the future to drive vsync events. Arc++ currently uses a custom
protocol for this that also rely on vsync manager but the plan is to replace
that with this upstream presentation-time protocol.

   window_->layer()->SetShowSolidColorContent();
 
   frame_callbacks_.splice(frame_callbacks_.end(), pending_frame_callbacks_);