Avoid dart:io dependency in try

tests/compiler/dart2js/mock_compiler.dart

Index: tests/compiler/dart2js/mock_compiler.dart
diff --git a/tests/compiler/dart2js/mock_compiler.dart b/tests/compiler/dart2js/mock_compiler.dart
index 4ae9430a65d46c43a356bc6ca87533b377cafb7c..184463c4be43d9d0275d5261ea3a16206df89a98 100644
--- a/tests/compiler/dart2js/mock_compiler.dart
+++ b/tests/compiler/dart2js/mock_compiler.dart
@@ -437,3 +437,31 @@ class MockElement extends FunctionElementX {
 
   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;
+}