Process all resolver treeshaked elements in Dart backend.

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 e2553ae7a7b54d86c0eed60051f1a3a0500123aa..4d1b2e07b28cdee9e98c00a98c2a6ab735aac235 100644
--- a/lib/compiler/implementation/compiler.dart
+++ b/lib/compiler/implementation/compiler.dart
@@ -233,7 +233,6 @@ class Compiler implements DiagnosticListener {
   DietParserTask dietParser;
   ParserTask parser;
   TreeValidatorTask validator;
-  UnparseValidator unparseValidator;
   ResolverTask resolver;
   TypeCheckerTask checker;
   Backend backend;
@@ -271,15 +270,14 @@ class Compiler implements DiagnosticListener {
     dietParser = new DietParserTask(this);
     parser = new ParserTask(this);
     validator = new TreeValidatorTask(this);
-    unparseValidator = new UnparseValidator(this, validateUnparse);
     resolver = new ResolverTask(this);
     checker = new TypeCheckerTask(this);
     backend = emitJavascript ?
         new JavaScriptBackend(this, generateSourceMap) :
-        new dart_backend.DartBackend(this);
+        new dart_backend.DartBackend(this, validateUnparse);
     enqueuer = new EnqueueTask(this);
     tasks = [scanner, dietParser, parser, resolver, checker,
-             unparseValidator, constantHandler, enqueuer];
+             constantHandler, enqueuer];
     tasks.addAll(backend.tasks);
   }
 
@@ -607,7 +605,6 @@ class Compiler implements DiagnosticListener {
     assert(parser !== null);
     Node tree = parser.parse(element);
     validator.validate(tree);
-    unparseValidator.check(element);
     elements = resolver.resolve(element);
     checker.check(tree, elements);
     return elements;