DDC: mostly incremental compilation, fixes #223

test/end_to_end_test.dart

 // Copyright (c) 2015, 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.
 
 /// Tests that run the checker end-to-end using the file system, but with a mock
 /// SDK.
 library dev_compiler.test.end_to_end;
 
 import 'package:dev_compiler/devc.dart';
 import 'package:dev_compiler/src/options.dart';
 import 'package:test/test.dart';
 import 'testing.dart' show realSdkContext, testDirectory;
 
 main() {
   var mockSdkContext = createAnalysisContextWithSources(
       new StrongModeOptions(), new SourceResolverOptions(useMockSdk: true));
-  var compiler = new BatchCompiler(mockSdkContext, new CompilerOptions());
-  _check(file) => compiler.compileFromUriString('$testDirectory/$file.dart');
+  BatchCompiler compiler;
+  _check(file) {
+    if (compiler == null) {
+      compiler = new BatchCompiler(mockSdkContext, new CompilerOptions());
+    }
+    compiler.compileFromUriString('$testDirectory/$file.dart');
+  }
 
   test('checker runs correctly (end-to-end)', () {
     _check('samples/funwithtypes');
   });
 
   test('checker accepts files with imports', () {
     _check('samples/import_test');
   });
 
   test('checker tests function types', () {
     // TODO(vsm): Check for correct down casts.
     _check('samples/function_type_test');
   });
 
   test('checker tests runtime checks', () {
     // TODO(sigmund,vsm): Check output for invalid checks.
     _check('samples/runtimetypechecktest');
   });
 
   test('checker tests return values', () {
     // TODO(vsm): Check for conversions.
     _check('samples/return_test');
   });
 }