Avoid dart:io dependency in try

tests/compiler/dart2js/mock_compiler.dart

 // Copyright (c) 2012, 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.
 
 library mock_compiler;
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:collection';
 
@@ skipping 419 matching lines @@
   MockElement(Element enclosingElement)
       : super('', ElementKind.FUNCTION, Modifiers.EMPTY,
               enclosingElement);
 
   get node => null;
 
   parseNode(_) => null;
 
   bool get hasNode => false;
 }
+
+// TODO(herhut): Disallow warnings and errors during compilation by default.
+MockCompiler compilerFor(String code, Uri uri,
+                         {bool analyzeAll: false,
+                          bool analyzeOnly: false,
+                          Map<String, String> coreSource,
+                          bool disableInlining: true,
+                          bool minify: false,
+                          bool trustTypeAnnotations: false,
+                          bool enableTypeAssertions: false,
+                          int expectedErrors,
+                          int expectedWarnings,
+                          api.CompilerOutputProvider outputProvider}) {
+  MockCompiler compiler = new MockCompiler.internal(
+      analyzeAll: analyzeAll,
+      analyzeOnly: analyzeOnly,
+      coreSource: coreSource,
+      disableInlining: disableInlining,
+      enableMinification: minify,
+      trustTypeAnnotations: trustTypeAnnotations,
+      enableTypeAssertions: enableTypeAssertions,
+      expectedErrors: expectedErrors,
+      expectedWarnings: expectedWarnings,
+      outputProvider: outputProvider);
+  compiler.registerSource(uri, code);
+  compiler.diagnosticHandler = createHandler(compiler, code);
+  return compiler;
+}