Decouple WorkItem from Compiler

pkg/compiler/lib/src/common/resolution.dart

Index: pkg/compiler/lib/src/common/resolution.dart
diff --git a/pkg/compiler/lib/src/common/resolution.dart b/pkg/compiler/lib/src/common/resolution.dart
index 9012c822c421e62cda59129e175bc4a6606ce944..2adfe261e94d278396406729510bd509ce4b457e 100644
--- a/pkg/compiler/lib/src/common/resolution.dart
+++ b/pkg/compiler/lib/src/common/resolution.dart
@@ -41,18 +41,24 @@ import 'backend_api.dart';
 import 'work.dart' show WorkItem;
 
 /// [WorkItem] used exclusively by the [ResolutionEnqueuer].
-class ResolutionWorkItem extends WorkItem {
+abstract class ResolutionWorkItem implements WorkItem {
+  factory ResolutionWorkItem(Resolution resolution, AstElement element) =
+      _ResolutionWorkItem;
+}
+
+class _ResolutionWorkItem extends WorkItem implements ResolutionWorkItem {
   bool _isAnalyzed = false;
+  final Resolution resolution;
 
-  ResolutionWorkItem(AstElement element) : super(element);
+  _ResolutionWorkItem(this.resolution, AstElement element) : super(element);
 
-  WorldImpact run(Compiler compiler, ResolutionEnqueuer world) {
-    WorldImpact impact = compiler.analyze(this, world);
+  WorldImpact run() {
+    assert(invariant(element, !_isAnalyzed,
+        message: 'Element ${element} has already been analyzed'));
+    WorldImpact impact = resolution.computeWorldImpact(element);
     _isAnalyzed = true;
     return impact;
   }
-
-  bool get isAnalyzed => _isAnalyzed;
 }
 
 class ResolutionImpact extends WorldImpact {
@@ -210,11 +216,8 @@ abstract class Resolution implements Frontend {
 
 /// A container of commonly used dependencies for tasks that involve parsing.
 abstract class ParsingContext {
-  factory ParsingContext(
-      DiagnosticReporter reporter,
-      ParserTask parser,
-      PatchParserTask patchParser,
-      Backend backend) = _ParsingContext;
+  factory ParsingContext(DiagnosticReporter reporter, ParserTask parser,
+      PatchParserTask patchParser, Backend backend) = _ParsingContext;
 
   DiagnosticReporter get reporter;
   ParserTask get parser;
@@ -238,8 +241,7 @@ class _ParsingContext implements ParsingContext {
   final PatchParserTask patchParser;
   final Backend backend;
 
-  _ParsingContext(this.reporter, this.parser,
-      this.patchParser, this.backend);
+  _ParsingContext(this.reporter, this.parser, this.patchParser, this.backend);
 
   @override
   measure(f()) => parser.measure(f);