cc: Remove SurfaceDependencies type

cc/surfaces/surface.cc

Index: cc/surfaces/surface.cc
diff --git a/cc/surfaces/surface.cc b/cc/surfaces/surface.cc
index 2ceae59329081c2295c5aadac3d04fb171d0742e..fffd5b7efdbc1e96dcb43cf9ec6aba6a8c1aeda0 100644
--- a/cc/surfaces/surface.cc
+++ b/cc/surfaces/surface.cc
@@ -220,13 +220,13 @@ void Surface::UpdateBlockingSurfaces(bool has_previous_pending_frame,
   // changes in dependencies so that we can update the SurfaceDependencyTracker
   // map.
   if (has_previous_pending_frame) {
-    SurfaceDependencies removed_dependencies;
+    base::flat_set<SurfaceId> removed_dependencies;
     for (const SurfaceId& surface_id : blocking_surfaces_) {
       if (!new_blocking_surfaces.count(surface_id))
         removed_dependencies.insert(surface_id);
     }
 
-    SurfaceDependencies added_dependencies;
+    base::flat_set<SurfaceId> added_dependencies;
     for (const SurfaceId& surface_id : new_blocking_surfaces) {
       if (!blocking_surfaces_.count(surface_id))
         added_dependencies.insert(surface_id);