Start actually adding incrementality into incremental kernel generator.

pkg/front_end/test/subpackage_relationships_test.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/compiler_options.dart';
 import 'package:front_end/dependency_grapher.dart';
 import 'package:path/path.dart' as pathos;
@@ skipping 10 matching lines @@
 ///
 /// TODO(paulberry): stuff in lib/src shouldn't depend on lib; lib should just
 /// re-export stuff in lib/src.
 /// TODO(paulberry): remove dependencies on analyzer.
 final subpackageRules = {
   'lib': new SubpackageRules(mayImportAnalyzer: true, allowedDependencies: [
     'lib/src',
     'lib/src/base',
     'lib/src/fasta',
     'lib/src/fasta/dill',
-    'lib/src/fasta/kernel'
+    'lib/src/fasta/kernel',
+    'lib/src/incremental'
   ]),
   'lib/src': new SubpackageRules(mayImportAnalyzer: true, allowedDependencies: [
     'lib',
     'lib/src/base',
     'lib/src/fasta',
     "lib/src/fasta/dill",
     "lib/src/fasta/kernel",
     'lib/src/fasta/source',
     'lib/src/incremental',
   ]),
   'lib/src/base': new SubpackageRules(
-      mayImportAnalyzer: true, allowedDependencies: ['lib', "lib/src/fasta"]),
+      mayImportAnalyzer: true,
+      allowedDependencies: ['lib', "lib/src/fasta", 'lib/src/incremental']),
   'lib/src/codegen': new SubpackageRules(),
   'lib/src/fasta': new SubpackageRules(allowedDependencies: [
     'lib',
     'lib/src/fasta/builder',
     'lib/src/fasta/dill',
     'lib/src/fasta/kernel',
     'lib/src/fasta/parser',
     'lib/src/fasta/scanner',
     'lib/src/fasta/testing',
     'lib/src/fasta/util',
@@ skipping 231 matching lines @@
       if (subpackageRules[subpackage].allowSubdirs) {
         subpackageRules[subpackage].actuallyHasSubdirs = true;
       } else {
         problem('Uri $src is in a subfolder of $subpackage, but that '
             'subpackage does not allow dart files in subdirectories.');
       }
     }
     return subpackage;
   }
 }