cc::SurfaceDependencyTracker should not crash when a Display goes away

components/viz/frame_sinks/mojo_frame_sink_manager.cc

Index: components/viz/frame_sinks/mojo_frame_sink_manager.cc
diff --git a/components/viz/frame_sinks/mojo_frame_sink_manager.cc b/components/viz/frame_sinks/mojo_frame_sink_manager.cc
index 3e7f681a5b115e20f1d6b714e764b66ba4fbafc5..1c4cc82bc5109544b7cb4858f7b7d9616594da53 100644
--- a/components/viz/frame_sinks/mojo_frame_sink_manager.cc
+++ b/components/viz/frame_sinks/mojo_frame_sink_manager.cc
@@ -26,10 +26,15 @@ MojoFrameSinkManager::MojoFrameSinkManager(bool use_surface_references,
       display_provider_(display_provider),
       binding_(this) {
   manager_.AddObserver(this);
+  dependency_tracker_ = base::MakeUnique<cc::SurfaceDependencyTracker>(
+      &manager_, manager_.GetPrimaryBeginFrameSource());
+  manager_.SetDependencyTracker(dependency_tracker_.get());
 }
 
 MojoFrameSinkManager::~MojoFrameSinkManager() {
   DCHECK(thread_checker_.CalledOnValidThread());
+  manager_.SetDependencyTracker(nullptr);
+  dependency_tracker_.reset();
   manager_.RemoveObserver(this);
 }
 
@@ -57,16 +62,6 @@ void MojoFrameSinkManager::CreateRootCompositorFrameSink(
   std::unique_ptr<cc::Display> display = display_provider_->CreateDisplay(
       frame_sink_id, surface_handle, &begin_frame_source);
 
-  // Lazily inject a SurfaceDependencyTracker into SurfaceManager if surface
-  // synchronization is enabled.
-  if (!manager_.dependency_tracker() &&
-      base::CommandLine::ForCurrentProcess()->HasSwitch(
-          cc::switches::kEnableSurfaceSynchronization)) {
-    std::unique_ptr<cc::SurfaceDependencyTracker> dependency_tracker(
-        new cc::SurfaceDependencyTracker(&manager_, begin_frame_source.get()));
-    manager_.SetDependencyTracker(std::move(dependency_tracker));
-  }
-
   compositor_frame_sinks_[frame_sink_id] =
       base::MakeUnique<GpuRootCompositorFrameSink>(
           this, &manager_, frame_sink_id, std::move(display),