Move compile-time constant registrations to the backend.

sdk/lib/_internal/compiler/implementation/compiler.dart

Index: sdk/lib/_internal/compiler/implementation/compiler.dart
diff --git a/sdk/lib/_internal/compiler/implementation/compiler.dart b/sdk/lib/_internal/compiler/implementation/compiler.dart
index 4803e8640cc065f7f97b89bb24af61930b10b0c0..6f673a357f3f96ebf6633dd273a9c8746b5d74ce 100644
--- a/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -123,6 +123,13 @@ abstract class Backend {
   bool classNeedsRti(ClassElement cls);
   bool methodNeedsRti(FunctionElement function);
 
+
+  /// Called during codegen when [constant] has been used.
+  void registerCompileTimeConstant(Constant constant, TreeElements elements) {}
+
+  /// Called during post-processing when [constant] has been evaluated.
+  void registerMetadataConstant(Constant constant, TreeElements elements) {}
+
   /// Called during resolution to notify to the backend that a class is
   /// being instantiated.
   void registerInstantiatedClass(ClassElement cls,
@@ -257,10 +264,6 @@ abstract class Backend {
     return new Future.value();
   }
 
-  void registerMetadataInstantiatedType(DartType type, TreeElements elements) {}
-  void registerMetadataStaticUse(Element element) {}
-  void registerMetadataGetOfStaticFunction(FunctionElement element) {}
-
   /// Called by [MirrorUsageAnalyzerTask] after it has merged all @MirrorsUsed
   /// annotations. The arguments corresponds to the unions of the corresponding
   /// fields of the annotations.
@@ -529,7 +532,6 @@ abstract class Compiler implements DiagnosticListener {
   ti.TypesTask typesTask;
   Backend backend;
   ConstantHandler constantHandler;
-  ConstantHandler metadataHandler;
   EnqueueTask enqueuer;
   DeferredLoadTask deferredLoadTask;
   MirrorUsageAnalyzerTask mirrorUsageAnalyzerTask;
@@ -644,8 +646,6 @@ abstract class Compiler implements DiagnosticListener {
       enqueuer = new EnqueueTask(this)];
 
     tasks.addAll(backend.tasks);
-    metadataHandler = new ConstantHandler(
-        this, backend.constantSystem, isMetadata: true);
   }
 
   Universe get resolverWorld => enqueuer.resolution.universe;