Add library mapping.

dart/frog/tests/leg/src/mock_compiler.dart

Index: dart/frog/tests/leg/src/mock_compiler.dart
diff --git a/dart/frog/tests/leg/src/mock_compiler.dart b/dart/frog/tests/leg/src/mock_compiler.dart
index 20e1c8f9f37dfd122016fb5d79f65f1a7d3e8766..26754165c7bec37698062b362b5a1dfe56139829 100644
--- a/dart/frog/tests/leg/src/mock_compiler.dart
+++ b/dart/frog/tests/leg/src/mock_compiler.dart
@@ -7,7 +7,6 @@
 #import("../../../../lib/uri/uri.dart");
 
 #import("../../../leg/elements/elements.dart");
-#import("../../../leg/io/io.dart", prefix: 'io');
 #import("../../../leg/leg.dart");
 #import("../../../leg/tree/tree.dart");
 #import("../../../leg/util/util.dart");
@@ -57,7 +56,7 @@ class MockCompiler extends Compiler {
                 String helperSource = DEFAULT_HELPERLIB])
       : warnings = [], errors = [],
         sources = new Map<String, String>(),
-        super.withCurrentDirectory(io.getCurrentDirectory()) {
+        super() {
     Uri uri = new Uri(scheme: "source");
     var script = new Script(uri, new MockFile(coreSource));
     coreLibrary = new LibraryElement(script);