Decouple WorkItem from Compiler

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

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.universe.world_impact;
 
 import '../elements/elements.dart' show Element;
 import '../util/util.dart' show Setlet;
 import 'use.dart' show DynamicUse, StaticUse, TypeUse;
 
@@ skipping 15 matching lines @@
 
   Iterable<StaticUse> get staticUses => const <StaticUse>[];
 
   // TODO(johnniwinther): Replace this by called constructors with type
   // arguments.
   // TODO(johnniwinther): Collect all checked types for checked mode separately
   // to support serialization.
 
   Iterable<TypeUse> get typeUses => const <TypeUse>[];
 
+  bool get isEmpty => true;
+
   void apply(WorldImpactVisitor visitor) {
     staticUses.forEach(visitor.visitStaticUse);
     dynamicUses.forEach(visitor.visitDynamicUse);
     typeUses.forEach(visitor.visitTypeUse);
   }
 
   String toString() => dump(this);
 
   static String dump(WorldImpact worldImpact) {
     StringBuffer sb = new StringBuffer();
@@ skipping 21 matching lines @@
   void registerStaticUse(StaticUse staticUse);
 }
 
 class WorldImpactBuilderImpl extends WorldImpact implements WorldImpactBuilder {
   // TODO(johnniwinther): Do we benefit from lazy initialization of the
   // [Setlet]s?
   Set<DynamicUse> _dynamicUses;
   Set<StaticUse> _staticUses;
   Set<TypeUse> _typeUses;
 
+  @override
+  bool get isEmpty =>
+      _dynamicUses == null && _staticUses == null && _typeUses == null;
+
+  /// Copy uses in [impact] to this impact builder.
+  void addImpact(WorldImpact impact) {
+    if (impact.isEmpty) return;
+    impact.dynamicUses.forEach(registerDynamicUse);
+    impact.staticUses.forEach(registerStaticUse);
+    impact.typeUses.forEach(registerTypeUse);
+  }
+
   void registerDynamicUse(DynamicUse dynamicUse) {
     assert(dynamicUse != null);
     if (_dynamicUses == null) {
       _dynamicUses = new Setlet<DynamicUse>();
     }
     _dynamicUses.add(dynamicUse);
   }
 
   Iterable<DynamicUse> get dynamicUses {
     return _dynamicUses != null ? _dynamicUses : const <DynamicUse>[];
@@ skipping 80 matching lines @@
 class TransformedWorldImpact implements WorldImpact, WorldImpactBuilder {
   final WorldImpact worldImpact;
 
   Setlet<StaticUse> _staticUses;
   Setlet<TypeUse> _typeUses;
   Setlet<DynamicUse> _dynamicUses;
 
   TransformedWorldImpact(this.worldImpact);
 
   @override
+  bool get isEmpty {
+    return worldImpact.isEmpty &&
+        _staticUses == null &&
+        _typeUses == null &&
+        _dynamicUses == null;
+  }
+
+  @override
   Iterable<DynamicUse> get dynamicUses {
     return _dynamicUses != null ? _dynamicUses : worldImpact.dynamicUses;
   }
 
   void registerDynamicUse(DynamicUse dynamicUse) {
     if (_dynamicUses == null) {
       _dynamicUses = new Setlet<DynamicUse>();
       _dynamicUses.addAll(worldImpact.dynamicUses);
     }
     _dynamicUses.add(dynamicUse);
@@ skipping 103 matching lines @@
     }
   }
 
   @override
   void visitTypeUse(TypeUse use) {
     if (_visitTypeUse != null) {
       _visitTypeUse(use);
     }
   }
 }