cc: Remove SurfaceDependencies type

cc/surfaces/surface.h

 // 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.
 
 #ifndef CC_SURFACES_SURFACE_H_
 #define CC_SURFACES_SURFACE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 96 matching lines @@
   size_t GetDestructionDependencyCount() const {
     return destruction_dependencies_.size();
   }
 
   const std::vector<SurfaceId>* active_referenced_surfaces() const {
     return active_frame_data_
                ? &active_frame_data_->frame.metadata.referenced_surfaces
                : nullptr;
   }
 
-  const SurfaceDependencies& blocking_surfaces() const {
+  const base::flat_set<SurfaceId>& blocking_surfaces() const {
     return blocking_surfaces_;
   }
 
   bool HasActiveFrame() const { return active_frame_data_.has_value(); }
   bool HasPendingFrame() const { return pending_frame_data_.has_value(); }
 
   bool destroyed() const { return destroyed_; }
   void set_destroyed(bool destroyed) { destroyed_ = destroyed; }
 
  private:
@@ skipping 28 matching lines @@
   SurfaceId surface_id_;
   SurfaceId previous_frame_surface_id_;
   base::WeakPtr<SurfaceFactory> factory_;
 
   base::Optional<FrameData> pending_frame_data_;
   base::Optional<FrameData> active_frame_data_;
   int frame_index_;
   bool destroyed_;
   std::vector<SurfaceSequence> destruction_dependencies_;
 
-  SurfaceDependencies blocking_surfaces_;
+  base::flat_set<SurfaceId> blocking_surfaces_;
   base::ObserverList<PendingFrameObserver, true> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(Surface);
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_H_