Revert "Switch FE to use the libraries.json format."

pkg/front_end/lib/src/testing/compiler_common.dart

Index: pkg/front_end/lib/src/testing/compiler_common.dart
diff --git a/pkg/front_end/lib/src/testing/compiler_common.dart b/pkg/front_end/lib/src/testing/compiler_common.dart
index 675bbbf8ecdca7a24016cdc701dd6ef52f948ba5..02890026496c70c6b20c21e5a9360440d69e2aaa 100644
--- a/pkg/front_end/lib/src/testing/compiler_common.dart
+++ b/pkg/front_end/lib/src/testing/compiler_common.dart
@@ -85,9 +85,6 @@ Future<Null> setup(CompilerOptions options, Map<String, dynamic> sources,
     }
   });
   fs.entityForUri(toTestUri('.packages')).writeAsStringSync('');
-  fs
-      .entityForUri(invalidCoreLibsSpecUri)
-      .writeAsStringSync(_invalidLibrariesSpec);
   options
     ..verify = true
     ..fileSystem = new HybridFileSystem(fs)
@@ -108,22 +105,13 @@ Uri _defaultDir = Uri.parse('file:///a/b/c/');
 /// helpers above.
 Uri toTestUri(String relativePath) => _defaultDir.resolve(relativePath);
 
-/// Uri to a libraries specification file that purposely provides
-/// invalid Uris to dart:core and dart:async. Used by tests that want to ensure
-/// that the sdk libraries are not loaded from sources, but read from a .dill
-/// file.
-Uri invalidCoreLibsSpecUri = toTestUri('invalid_sdk_libraries.json');
-
-String _invalidLibrariesSpec = '''
-{
-  "vm": {
-    "libraries": {
-      "core":  {"uri": "/non_existing_file/core.dart"},
-      "async": {"uri": "/non_existing_file/async.dart"}
-    }
-  }
-}
-''';
+/// A map defining the location of core libraries that purposely provides
+/// invalid Uris. Used by tests that want to ensure that the sdk libraries are
+/// not loaded from sources, but read from a .dill file.
+Map<String, Uri> invalidCoreLibs = {
+  'core': Uri.parse('file:///non_existing_file/core.dart'),
+  'async': Uri.parse('file:///non_existing_file/async.dart'),
+};
 
 bool isDartCoreLibrary(Library lib) => isDartCore(lib.importUri);
 bool isDartCore(Uri uri) => uri.scheme == 'dart' && uri.path == 'core';