DDC: mostly incremental compilation, fixes #223

test/end_to_end_test.dart

Index: test/end_to_end_test.dart
diff --git a/test/end_to_end_test.dart b/test/end_to_end_test.dart
index 7515240816db7afd083bfb60b5cacbdaddf7d3f2..5dcfb1902d68a55de47f1178d3e351dc8c8bf84b 100644
--- a/test/end_to_end_test.dart
+++ b/test/end_to_end_test.dart
@@ -14,8 +14,13 @@ 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');