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 bf51eb7a1c4a8ee12d839c316677aecbf2256d27..87b0d5b6b379bd1d85720679af06521472ff4252 100644
--- a/lib/compiler/implementation/compiler.dart
+++ b/lib/compiler/implementation/compiler.dart
@@ -14,13 +14,21 @@ final bool REPORT_EXCESS_RESOLUTION = false;
  */
 final bool REPORT_PASS2_OPTIMIZATIONS = false;
 
+/**
+ * Contains backend-specific data that is used throughout the compilation of
+ * one work item.
+ */
+class ItemCompilationContext {
+}
+
 class WorkItem {
+  final ItemCompilationContext compilationContext;
   final Element element;
   TreeElements resolutionTree;
   bool allowSpeculativeOptimization = true;
   List<HTypeGuard> guards = const <HTypeGuard>[];
 
-  WorkItem(this.element, this.resolutionTree);
+  WorkItem(this.element, this.resolutionTree, this.compilationContext);
 
   bool isAnalyzed() => resolutionTree !== null;
 
@@ -49,6 +57,10 @@ class Backend {
                                      Collection<LibraryElement> libraries);
   abstract void assembleProgram();
   abstract List<CompilerTask> get tasks();
+
+  ItemCompilationContext createItemCompilationContext() {
+    return new ItemCompilationContext();
+  }
 }
 
 class Compiler implements DiagnosticListener {
@@ -920,7 +932,7 @@ class Tracer {
 
   const Tracer();
 
-  void traceCompilation(String methodName) {
+  void traceCompilation(String methodName, ItemCompilationContext context) {
   }
 
   void traceGraph(String name, var graph) {