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

components/exo/surface.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/exo/surface.h"
 
 #include <utility>
 
 #include "base/callback_helpers.h"
 #include "base/logging.h"
@@ skipping 187 matching lines @@
   window_->AddObserver(this);
   aura::Env::GetInstance()->context_factory()->AddObserver(this);
 }
 
 Surface::~Surface() {
   aura::Env::GetInstance()->context_factory()->RemoveObserver(this);
   for (SurfaceObserver& observer : observers_)
     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_);
   active_frame_callbacks_.splice(active_frame_callbacks_.end(),
                                  frame_callbacks_);
   // Call all frame callbacks with a null frame time to indicate that they
   // have been cancelled.
   for (const auto& frame_callback : active_frame_callbacks_)
     frame_callback.Run(base::TimeTicks());
 
@@ skipping 629 matching lines @@
 
 int64_t Surface::GetPropertyInternal(const void* key,
                                      int64_t default_value) const {
   std::map<const void*, Value>::const_iterator iter = prop_map_.find(key);
   if (iter == prop_map_.end())
     return default_value;
   return iter->second.value;
 }
 
 }  // namespace exo