No longer store the compilation-context in WorkItem.

pkg/compiler/lib/src/ssa/ssa.dart

 // Copyright (c) 2012, 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.
 
 library ssa;
 
 import '../common/codegen.dart' show CodegenWorkItem;
 import '../common/tasks.dart' show CompilerTask;
 import '../elements/elements.dart' show Element, FunctionElement;
 import '../io/source_information.dart';
 import '../js/js.dart' as js;
 import '../js_backend/backend.dart' show JavaScriptBackend, FunctionCompiler;
 
 import 'builder.dart';
 import 'builder_kernel.dart';
 import 'codegen.dart';
+import 'context.dart';
 import 'nodes.dart';
 import 'optimize.dart';
 
 class SsaFunctionCompiler implements FunctionCompiler {
   final SsaCodeGeneratorTask generator;
   final SsaBuilderTask builder;
   final SsaKernelBuilderTask builderKernel;
   final SsaOptimizerTask optimizer;
   final JavaScriptBackend backend;
   final bool useKernel;
 
   SsaFunctionCompiler(JavaScriptBackend backend,
       SourceInformationStrategy sourceInformationFactory, this.useKernel)
       : generator = new SsaCodeGeneratorTask(backend, sourceInformationFactory),
         builder = new SsaBuilderTask(backend, sourceInformationFactory),
         builderKernel =
             new SsaKernelBuilderTask(backend, sourceInformationFactory),
         optimizer = new SsaOptimizerTask(backend),
         backend = backend;
 
   /// Generates JavaScript code for `work.element`.
   /// Using the ssa builder, optimizer and codegenerator.
   js.Fun compile(CodegenWorkItem work) {
-    HGraph graph = useKernel ? builderKernel.build(work) : builder.build(work);
-    optimizer.optimize(work, graph);
+    var context = new SsaCompilationContext();
+    HGraph graph = useKernel
+      ? builderKernel.build(work, context)
+      : builder.build(work, context);
+    optimizer.optimize(graph, work, context);
     Element element = work.element;
     js.Expression result = generator.generateCode(work, graph);
     if (element is FunctionElement) {
       // TODO(sigmund): replace by kernel transformer when `useKernel` is true.
       result = backend.rewriteAsync(element, result);
     }
     return result;
   }
 
   Iterable<CompilerTask> get tasks {
     return <CompilerTask>[
       useKernel ? builderKernel : builder,
       optimizer,
       generator
     ];
   }
 }