Introduce benign errors.

tests/compiler/dart2js/benign_error_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.
+
+// Test that benign error do not prevent compilation.
+
+import 'memory_compiler.dart';
+
+import 'package:async_helper/async_helper.dart';
+import 'package:compiler/src/compiler.dart';
+import 'package:compiler/src/diagnostics/messages.dart';
+import 'package:compiler/src/js_backend/js_backend.dart';
+import 'package:expect/expect.dart';
+
+main() {
+  asyncTest(() async {
+    for (MessageKind kind in Compiler.BENIGN_ERRORS) {
+      await testExamples(kind);
+    }
+  });
+}
+
+testExamples(MessageKind kind) async {
+  MessageTemplate template = MessageTemplate.TEMPLATES[kind];
+  for (var example in template.examples) {
+    if (example is! Map) {
+      example = {'main.dart': example};
+    }
+    DiagnosticCollector collector = new DiagnosticCollector();
+    CompilationResult result = await runCompiler(
+        memorySourceFiles: example,
+        diagnosticHandler: collector);
+    Expect.isTrue(result.isSuccess);
+    Expect.isTrue(
+        collector.errors.any((message) => message.messageKind == kind));
+    Compiler compiler = result.compiler;
+    JavaScriptBackend backend = compiler.backend;
+    Expect.isNotNull(backend.generatedCode[compiler.mainFunction]);
+  }
+}