Add model test of CodegenWorldBuilder to compile_from_dill_test

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

Index: pkg/compiler/lib/src/universe/codegen_world_builder.dart
diff --git a/pkg/compiler/lib/src/universe/codegen_world_builder.dart b/pkg/compiler/lib/src/universe/codegen_world_builder.dart
index d937594b74bf1e0b939c6dea2028c5f591dd876b..0d17a9ef32835279f5b72348c83ae7ca2e782b78 100644
--- a/pkg/compiler/lib/src/universe/codegen_world_builder.dart
+++ b/pkg/compiler/lib/src/universe/codegen_world_builder.dart
@@ -97,14 +97,22 @@ abstract class CodegenWorldBuilderImpl implements CodegenWorldBuilder {
   final Map<ClassEntity, _ClassUsage> _processedClasses =
       <ClassEntity, _ClassUsage>{};
 
+  Map<ClassEntity, _ClassUsage> get classUsageForTesting => _processedClasses;
+
   /// Map of registered usage of static members of live classes.
   final Map<Entity, _StaticMemberUsage> _staticMemberUsage =
       <Entity, _StaticMemberUsage>{};
 
+  Map<Entity, _StaticMemberUsage> get staticMemberUsageForTesting =>
+      _staticMemberUsage;
+
   /// Map of registered usage of instance members of live classes.
   final Map<MemberEntity, _MemberUsage> _instanceMemberUsage =
       <MemberEntity, _MemberUsage>{};
 
+  Map<MemberEntity, _MemberUsage> get instanceMemberUsageForTesting =>
+      _instanceMemberUsage;
+
   /// Map containing instance members of live classes that are not yet live
   /// themselves.
   final Map<String, Set<_MemberUsage>> _instanceMembersByName =