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

cc/surfaces/surface.cc

 // Copyright 2014 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 "cc/surfaces/surface.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 90 matching lines @@
       frame_sink_ids_for_dependencies.insert(surface_id.frame_sink_id());
     for (const SurfaceId& surface_id : frame.metadata.referenced_surfaces) {
       // A surface ID in |referenced_surfaces| that has a corresponding surface
       // ID in |activation_dependencies| with the same frame sink ID is said to
       // be a fallback surface that can be used in place of the primary surface
       // if the deadline passes before the dependency becomes available.
       bool is_fallback_surface =
           frame_sink_ids_for_dependencies.count(surface_id.frame_sink_id()) > 0;
       if (is_fallback_surface) {
         Surface* surface = surface_manager_->GetSurfaceForId(surface_id);
-        DCHECK(surface);
-        surface->Close();
+        // A misbehaving client may report a non-existent surface ID as a
+        // |referenced_surface|. In that case, |surface| would be nullptr, and
+        // there is nothing to do here.
+        if (surface)
+          surface->Close();
       }
     }
     pending_frame_data_ =
         FrameData(std::move(frame), callback, will_draw_callback);
     // Ask the surface manager to inform |this| when its dependencies are
     // resolved.
     surface_manager_->RequestSurfaceResolution(this);
   } else {
     // If there are no blockers, then immediately activate the frame.
     ActivateFrame(FrameData(std::move(frame), callback, will_draw_callback));
@@ skipping 255 matching lines @@
     frame->metadata.latency_info.swap(*latency_info);
     return;
   }
   std::copy(frame->metadata.latency_info.begin(),
             frame->metadata.latency_info.end(),
             std::back_inserter(*latency_info));
   frame->metadata.latency_info.clear();
 }
 
 }  // namespace cc