Add ConstantUse to WorldImpact

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

Index: pkg/compiler/lib/src/universe/resolution_world_builder.dart
diff --git a/pkg/compiler/lib/src/universe/resolution_world_builder.dart b/pkg/compiler/lib/src/universe/resolution_world_builder.dart
index 4fb573bd79f91dd3d3870439859b8bdabe465989..6095664c177c3bb2a0ea6b8829583c16cf5c7023 100644
--- a/pkg/compiler/lib/src/universe/resolution_world_builder.dart
+++ b/pkg/compiler/lib/src/universe/resolution_world_builder.dart
@@ -89,6 +89,10 @@ abstract class ResolutionEnqueuerWorldBuilder extends ResolutionWorldBuilder {
   /// Applies the [staticUse] to applicable members. Calls [membersUsed] with
   /// the usage changes for each member.
   void registerStaticUse(StaticUse staticUse, MemberUsedCallback memberUsed);
+
+  /// Register the constant [use] with this world builder. Returns `true` if
+  /// the constant use was new to the world.
+  bool registerConstantUse(ConstantUse use);
 }
 
 /// The type and kind of an instantiation registered through
@@ -355,6 +359,8 @@ class ElementResolutionWorldBuilder implements ResolutionEnqueuerWorldBuilder {
       <ClassElement, ClassHierarchyNode>{};
   final Map<ClassElement, ClassSet> _classSets = <ClassElement, ClassSet>{};
 
+  final Set<ConstantValue> _constantValues = new Set<ConstantValue>();
+
   bool get isClosed => _closed;
 
   ElementResolutionWorldBuilder(
@@ -610,6 +616,10 @@ class ElementResolutionWorldBuilder implements ResolutionEnqueuerWorldBuilder {
     isChecks.add(type);
   }
 
+  bool registerConstantUse(ConstantUse use) {
+    return _constantValues.add(use.value);
+  }
+
   void registerStaticUse(StaticUse staticUse, MemberUsedCallback memberUsed) {
     Element element = staticUse.element;
     assert(invariant(element, element.isDeclaration,