Split backend implementation of EnqueuerListener

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

Index: pkg/compiler/lib/src/js_backend/backend_usage.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend_usage.dart b/pkg/compiler/lib/src/js_backend/backend_usage.dart
index b99358bd026a5f8f857dc2db517cb1377bf1f123..f1d25c3682d2b3dcc0ea8609e878a94c7d77b3df 100644
--- a/pkg/compiler/lib/src/js_backend/backend_usage.dart
+++ b/pkg/compiler/lib/src/js_backend/backend_usage.dart
@@ -20,6 +20,21 @@ abstract class BackendUsage {
   bool get needToInitializeDispatchProperty;
   bool usedByBackend(Element element);
   Iterable<Element> get globalDependencies;
+
+  /// `true` if a core-library function requires the preamble file to function.
+  bool get requiresPreamble;
+
+  /// `true` if [BackendHelpers.invokeOnMethod] is used.
+  bool get isInvokeOnUsed;
+
+  /// `true` of `Object.runtimeType` is used.
+  bool get isRuntimeTypeUsed;
+
+  /// `true` if the `dart:isolate` library is in use.
+  bool get isIsolateInUse;
+
+  /// `true` if `Function.apply` is used.
+  bool get isFunctionApplyUsed;
 }
 
 abstract class BackendUsageBuilder {
@@ -35,6 +50,15 @@ abstract class BackendUsageBuilder {
       {bool isGlobal: false});
   WorldImpact createImpactFor(BackendImpact impact);
   void registerUsedMember(MemberElement member);
+
+  /// `true` of `Object.runtimeType` is used.
+  bool isRuntimeTypeUsed;
+
+  /// `true` if the `dart:isolate` library is in use.
+  bool isIsolateInUse;
+
+  /// `true` if `Function.apply` is used.
+  bool isFunctionApplyUsed;
 }
 
 class BackendUsageImpl implements BackendUsage, BackendUsageBuilder {
@@ -50,6 +74,21 @@ class BackendUsageImpl implements BackendUsage, BackendUsageBuilder {
   bool _needToInitializeIsolateAffinityTag = false;
   bool _needToInitializeDispatchProperty = false;
 
+  /// `true` if a core-library function requires the preamble file to function.
+  bool requiresPreamble = false;
+
+  /// `true` if [BackendHelpers.invokeOnMethod] is used.
+  bool isInvokeOnUsed = false;
+
+  /// `true` of `Object.runtimeType` is used.
+  bool isRuntimeTypeUsed = false;
+
+  /// `true` if the `dart:isolate` library is in use.
+  bool isIsolateInUse = false;
+
+  /// `true` if `Function.apply` is used.
+  bool isFunctionApplyUsed = false;
+
   BackendUsageImpl(this._commonElements, this._helpers, this._resolution);
 
   bool get needToInitializeIsolateAffinityTag =>
@@ -196,6 +235,12 @@ class BackendUsageImpl implements BackendUsage, BackendUsageBuilder {
   void registerUsedMember(MemberElement member) {
     if (member == _helpers.getIsolateAffinityTagMarker) {
       _needToInitializeIsolateAffinityTag = true;
+    } else if (member == _helpers.requiresPreambleMarker) {
+      requiresPreamble = true;
+    } else if (member == _helpers.invokeOnMethod) {
+      isInvokeOnUsed = true;
+    } else if (_commonElements.isFunctionApplyMethod(member)) {
+      isFunctionApplyUsed = true;
     }
   }