Add generic types to Sort and Comparable. Fix crasher bug in codegen.

lib/src/compiler/code_generator.dart

Index: lib/src/compiler/code_generator.dart
diff --git a/lib/src/compiler/code_generator.dart b/lib/src/compiler/code_generator.dart
index ba65adf354cb69cffa88c9b4bcc8fb43bc2759e8..3ea5a2254ef071e5b2ba29821bdd2b99ba14b4ba 100644
--- a/lib/src/compiler/code_generator.dart
+++ b/lib/src/compiler/code_generator.dart
@@ -3111,7 +3111,7 @@ class CodeGenerator extends GeneralizingAstVisitor
       var args = _visit(argumentList) as List<JS.Expression>;
       return isFactory ? new JS.Call(ctor, args) : new JS.New(ctor, args);
     }
-    if (_isObjectLiteral(element.enclosingElement)) {
+    if (element != null && _isObjectLiteral(element.enclosingElement)) {
       return _emitObjectLiteral(argumentList);
     }
     if (isConst) return _emitConst(emitNew);