Add an incremental reloader example and a utility tool to trigger a reload by

pkg/front_end/lib/src/incremental_kernel_generator_impl.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:front_end/file_system.dart';
 import 'package:front_end/incremental_kernel_generator.dart';
 import 'package:front_end/src/base/api_signature.dart';
 import 'package:front_end/src/base/performace_logger.dart';
 import 'package:front_end/src/base/processed_options.dart';
 import 'package:front_end/src/fasta/dill/dill_library_builder.dart';
 import 'package:front_end/src/fasta/dill/dill_target.dart';
 import 'package:front_end/src/fasta/kernel/kernel_target.dart';
 import 'package:front_end/src/fasta/ticker.dart';
 import 'package:front_end/src/fasta/translate_uri.dart';
 import 'package:front_end/src/incremental/byte_store.dart';
 import 'package:front_end/src/incremental/file_state.dart';
 import 'package:kernel/binary/ast_from_binary.dart';
 import 'package:kernel/binary/limited_ast_to_binary.dart';
 import 'package:kernel/kernel.dart' hide Source;
 import 'package:kernel/target/targets.dart' show TargetFlags;
 import 'package:kernel/target/vm_fasta.dart' show VmFastaTarget;
 
-dynamic unimplemented() {
-  // TODO(paulberry): get rid of this.
-  throw new UnimplementedError();
-}
-
 class ByteSink implements Sink<List<int>> {
   final BytesBuilder builder = new BytesBuilder();
 
   void add(List<int> data) {
     builder.add(data);
   }
 
   void close() {}
 }
 
@@ skipping 85 matching lines @@
         for (Library library in result.kernelLibraries) {
           Uri uri = library.importUri;
           if (_latestSignature[uri] != result.signature) {
             _latestSignature[uri] = result.signature;
             program.libraries.add(library);
             library.parent = program;
           }
         }
       }
 
+      if (watch != null) _fsState.fileUris.forEach((f) => watch(f, true));
+
       // TODO(scheglov) Add libraries which import changed libraries.
       // For now the corresponding test works because we use full library
       // contents to compute signatures (not just API parts). So, every library
       // that imports a changed one, is affected.
 
       // Set the main method.
       for (var library in program.libraries) {
         if (library.fileUri == _entryPoint.toString()) {
           program.mainMethod = library.procedures.firstWhere(
               (procedure) => procedure.name.name == 'main',
               orElse: () => null);
           break;
         }
       }
 
       return new DeltaProgram(program);
     });
   }
 
   @override
   void invalidate(Uri uri) {
     _invalidatedFiles.add(uri);
   }
 
   @override
-  void invalidateAll() => unimplemented();
+  void invalidateAll() {
+    _invalidatedFiles.addAll(_fsState.fileUris);
+  }
 
   /// Ensure that [dillTarget] includes the [cycle] libraries.  It already
   /// contains all the libraries that sorted before the given [cycle] in
   /// topological order.  Return the result with the cycle libraries.
   Future<_LibraryCycleResult> _compileCycle(
       CanonicalName nameRoot, DillTarget dillTarget, LibraryCycle cycle) async {
     return _logger.runAsync('Compile cycle $cycle', () async {
       String signature;
       {
         var signatureBuilder = new ApiSignature();
@@ skipping 154 matching lines @@
   /// TODO(scheglov) Use API signatures.
   /// TODO(scheglov) Or use tree shaking and compute signatures of outlines.
   final String signature;
 
   /// Kernel libraries for libraries in the [cycle].  Bodies of dependencies
   /// are not included, but but references to those dependencies are included.
   final List<Library> kernelLibraries;
 
   _LibraryCycleResult(this.cycle, this.signature, this.kernelLibraries);
 }