Support enabling type checker.

pkg/compiler/lib/src/typechecker.dart

Index: pkg/compiler/lib/src/typechecker.dart
diff --git a/pkg/compiler/lib/src/typechecker.dart b/pkg/compiler/lib/src/typechecker.dart
index 12015f29c707c9991c0a1f9eb623172f6f647680..1340fa25e799f3fe39ef0dd28f15bccf235de9b6 100644
--- a/pkg/compiler/lib/src/typechecker.dart
+++ b/pkg/compiler/lib/src/typechecker.dart
@@ -51,15 +51,13 @@ class TypeCheckerTask extends CompilerTask {
   TypeCheckerTask(Compiler compiler) : super(compiler);
   String get name => "Type checker";
 
+  bool enabled = false;
+
   void check(AstElement element) {
-    return;
+    if (!enabled) return;
     if (element.isClass) return;
     if (element.isTypedef) return;
     ResolvedAst resolvedAst = element.resolvedAst;
-    if (resolvedAst.node == null) {
-      return;
-      new FiskFisk();
-    }
     reporter.withCurrentElement(element.implementation, () {
       measure(() {
         TypeCheckerVisitor visitor = new TypeCheckerVisitor(