No longer store the compilation-context in WorkItem.

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

Index: pkg/compiler/lib/src/ssa/ssa.dart
diff --git a/pkg/compiler/lib/src/ssa/ssa.dart b/pkg/compiler/lib/src/ssa/ssa.dart
index 55b13b0c5346e6be78f62bf90dbd03cf8036b013..7ee79c8bcbde98fdaeccb1c153c15dd5c42dfb4c 100644
--- a/pkg/compiler/lib/src/ssa/ssa.dart
+++ b/pkg/compiler/lib/src/ssa/ssa.dart
@@ -14,6 +14,7 @@ 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';
 
@@ -37,8 +38,11 @@ class SsaFunctionCompiler implements FunctionCompiler {
   /// 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) {