Start implementing logic for determining when formal parameters need type checks.

pkg/front_end/lib/src/fasta/kernel/kernel_target.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.kernel_target;
 
 import 'dart:async' show Future;
 
 import 'package:kernel/ast.dart'
     show
@@ skipping 235 matching lines @@
       installDefaultSupertypes();
       installDefaultConstructors(sourceClasses);
       loader.resolveConstructors();
       loader.finishTypeVariables(objectClassBuilder);
       program =
           link(new List<Library>.from(loader.libraries), nameRoot: nameRoot);
       loader.computeHierarchy(program);
       loader.checkOverrides(sourceClasses);
       loader.prepareInitializerInference();
       loader.performInitializerInference();
+      loader.computeFormalSafety();
     } on deprecated_InputError catch (e) {
       handleInputError(e, isFullProgram: false);
     } catch (e, s) {
       return reportCrash(e, s, loader?.currentUriForCrashReporting);
     }
     return program;
   }
 
   /// Build the kernel representation of the program loaded by this target. The
   /// program will contain full bodies for the code loaded from sources, and
@@ skipping 404 matching lines @@
   }
   for (Constructor constructor in superclass.constructors) {
     if (constructor.name.name.isEmpty) {
       return constructor.function.requiredParameterCount == 0
           ? constructor
           : null;
     }
   }
   return null;
 }