Move types out of the HInstructions.

lib/compiler/implementation/compiler.dart

Index: lib/compiler/implementation/compiler.dart
diff --git a/lib/compiler/implementation/compiler.dart b/lib/compiler/implementation/compiler.dart
index ca6ca2ba8cb60374a28e6029a5089e9d50e33292..e4f38156cb3b7fcefadc91849b3e83cd5679b18d 100644
--- a/lib/compiler/implementation/compiler.dart
+++ b/lib/compiler/implementation/compiler.dart
@@ -49,6 +49,18 @@ class Backend {
                                      Collection<LibraryElement> libraries);
   abstract void assembleProgram();
   abstract List<CompilerTask> get tasks();
+
+  WorkItem createWorkItem(Element element, TreeElements elements) {
+    return new WorkItem(element, elements);
+  }
+}
+
+class JavaScriptWorkItem extends WorkItem {
+  HTypeMap types;
+
+  JavaScriptWorkItem(Element element, TreeElements elements)
+      : types = new HTypeMap(),
+        super(element, elements);
 }
 
 class JavaScriptBackend extends Backend {
@@ -204,6 +216,10 @@ class JavaScriptBackend extends Backend {
     if (!fields.containsKey(field)) return HType.CONFLICTING;
     return fields[field];
   }
+
+  JavaScriptWorkItem createWorkItem(Element element, TreeElements elements) {
+    return new JavaScriptWorkItem(element, elements);
+  }
 }
 
 class Compiler implements DiagnosticListener {
@@ -1072,7 +1088,7 @@ class Tracer {
 
   const Tracer();
 
-  void traceCompilation(String methodName) {
+  void traceCompilation(String methodName, WorkItem work) {
   }
 
   void traceGraph(String name, var graph) {