Revert "Move towards using WorldImpact for codegen"

pkg/compiler/lib/src/universe/world_impact.dart

Index: pkg/compiler/lib/src/universe/world_impact.dart
diff --git a/pkg/compiler/lib/src/universe/world_impact.dart b/pkg/compiler/lib/src/universe/world_impact.dart
index 723a87af8bddcdc817f0589bd60adc1db38f080e..99c1c3c129c339086edae64724c094a5e55c4095 100644
--- a/pkg/compiler/lib/src/universe/world_impact.dart
+++ b/pkg/compiler/lib/src/universe/world_impact.dart
@@ -61,18 +61,12 @@ class WorldImpact {
   }
 }
 
-abstract class WorldImpactBuilder {
-  void registerDynamicUse(DynamicUse dynamicUse);
-  void registerTypeUse(TypeUse typeUse);
-  void registerStaticUse(StaticUse staticUse);
-}
-
-class WorldImpactBuilderImpl extends WorldImpact implements WorldImpactBuilder {
+class WorldImpactBuilder {
   // TODO(johnniwinther): Do we benefit from lazy initialization of the
   // [Setlet]s?
-  Set<DynamicUse> _dynamicUses;
-  Set<StaticUse> _staticUses;
-  Set<TypeUse> _typeUses;
+  Setlet<DynamicUse> _dynamicUses;
+  Setlet<StaticUse> _staticUses;
+  Setlet<TypeUse> _typeUses;
 
   void registerDynamicUse(DynamicUse dynamicUse) {
     assert(dynamicUse != null);
@@ -111,60 +105,9 @@ class WorldImpactBuilderImpl extends WorldImpact implements WorldImpactBuilder {
   }
 }
 
-/// [WorldImpactBuilder] that can create and collect a sequence of
-/// [WorldImpact]s.
-class StagedWorldImpactBuilder implements WorldImpactBuilder {
-  final bool collectImpacts;
-  WorldImpactBuilderImpl _currentBuilder;
-  List<WorldImpactBuilderImpl> _builders = <WorldImpactBuilderImpl>[];
-
-  StagedWorldImpactBuilder({this.collectImpacts: false});
-
-  void _ensureBuilder() {
-    if (_currentBuilder == null) {
-      _currentBuilder = new WorldImpactBuilderImpl();
-      if (collectImpacts) {
-        _builders.add(_currentBuilder);
-      }
-    }
-  }
-
-  @override
-  void registerTypeUse(TypeUse typeUse) {
-    _ensureBuilder();
-    _currentBuilder.registerTypeUse(typeUse);
-  }
-
-  @override
-  void registerDynamicUse(DynamicUse dynamicUse) {
-    _ensureBuilder();
-    _currentBuilder.registerDynamicUse(dynamicUse);
-  }
-
-  @override
-  void registerStaticUse(StaticUse staticUse) {
-    _ensureBuilder();
-    _currentBuilder.registerStaticUse(staticUse);
-  }
-
-  /// Returns the [WorldImpact] built so far with this builder. The builder
-  /// is reset, and if [collectImpacts] is `true` the impact is cached for
-  /// [worldImpacts].
-  WorldImpact flush() {
-    if (_currentBuilder == null) return const WorldImpact();
-    WorldImpact worldImpact = _currentBuilder;
-    _currentBuilder = null;
-    return worldImpact;
-  }
-
-  /// If [collectImpacts] is `true` this returns all [WorldImpact]s built with
-  /// this builder.
-  Iterable<WorldImpact> get worldImpacts => _builders;
-}
-
 /// Mutable implementation of [WorldImpact] used to transform
 /// [ResolutionImpact] or [CodegenImpact] to [WorldImpact].
-class TransformedWorldImpact implements WorldImpact, WorldImpactBuilder {
+class TransformedWorldImpact implements WorldImpact {
   final WorldImpact worldImpact;
 
   Setlet<StaticUse> _staticUses;