Move global dependencies to BackendUsage

pkg/compiler/lib/src/js_backend/backend_usage.dart

 // Copyright (c) 2017, 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.
 
 import '../common.dart';
 import '../common/resolution.dart' show Resolution;
-import '../compiler.dart' show GlobalDependencyRegistry;
 import '../core_types.dart';
 import '../elements/elements.dart';
 import '../elements/resolution_types.dart';
 import '../universe/selector.dart';
 import '../universe/use.dart';
 import '../universe/world_impact.dart'
     show WorldImpact, WorldImpactBuilder, WorldImpactBuilderImpl;
+import '../util/util.dart' show Setlet;
 import 'backend_helpers.dart';
 import 'backend_impact.dart';
 
 class BackendUsage {
   final CommonElements commonElements;
   final BackendHelpers helpers;
   final Resolution resolution;
-  final GlobalDependencyRegistry globalDependencies;
+  // TODO(johnniwinther): Remove the need for this.
+  Setlet<Element> _globalDependencies;
 
   /// List of elements that the backend may use.
   final Set<Element> helpersUsed = new Set<Element>();
 
   bool needToInitializeIsolateAffinityTag = false;
   bool needToInitializeDispatchProperty = false;
 
-  BackendUsage(this.commonElements, this.helpers, this.resolution,
-      this.globalDependencies);
+  BackendUsage(this.commonElements, this.helpers, this.resolution);
 
   /// The backend must *always* call this method when enqueuing an
   /// element. Calls done by the backend are not seen by global
   /// optimizations, so they would make these optimizations unsound.
   /// Therefore we need to collect the list of helpers the backend may
   /// use.
   // TODO(johnniwinther): Replace this with a more precise modelling; type
   // inference of these elements is disabled.
   Element registerBackendUse(Element element) {
     if (element == null) return null;
@@ skipping 62 matching lines @@
   }
 
   void registerBackendStaticUse(
       WorldImpactBuilder worldImpact, MethodElement element,
       {bool isGlobal: false}) {
     registerBackendUse(element);
     worldImpact.registerStaticUse(
         // TODO(johnniwinther): Store the correct use in impacts.
         new StaticUse.foreignUse(element));
     if (isGlobal) {
-      globalDependencies.registerDependency(element);
+      registerGlobalDependency(element);
     }
   }
 
   void registerBackendInstantiation(
       WorldImpactBuilder worldImpact, ClassElement cls,
       {bool isGlobal: false}) {
     cls.ensureResolved(resolution);
     registerBackendUse(cls);
     worldImpact.registerTypeUse(new TypeUse.instantiation(cls.rawType));
     if (isGlobal) {
-      globalDependencies.registerDependency(cls);
+      registerGlobalDependency(cls);
     }
   }
 
   void registerBackendImpact(
       WorldImpactBuilder worldImpact, BackendImpact backendImpact) {
     for (Element staticUse in backendImpact.staticUses) {
       assert(staticUse != null);
       registerBackendStaticUse(worldImpact, staticUse);
     }
     for (Element staticUse in backendImpact.globalUses) {
@@ skipping 22 matching lines @@
       switch (feature) {
         case BackendFeature.needToInitializeDispatchProperty:
           needToInitializeDispatchProperty = true;
           break;
         case BackendFeature.needToInitializeIsolateAffinityTag:
           needToInitializeIsolateAffinityTag = true;
           break;
       }
     }
   }
+
+  void registerGlobalDependency(Element element) {
+    if (element == null) return;
+    if (_globalDependencies == null) {
+      _globalDependencies = new Setlet<Element>();
+    }
+    _globalDependencies.add(element.implementation);
+  }
+
+  Iterable<Element> get globalDependencies => _globalDependencies;
 }