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

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

 // Copyright (c) 2017, 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.
 
 /// Common compiler options and helper functions used for testing.
 library front_end.testing.compiler_options_common;
 
 import 'dart:async';
 
 import 'package:front_end/front_end.dart';
@@ skipping 67 matching lines @@
   var fs = new MemoryFileSystem(_defaultDir);
   sources.forEach((name, data) {
     var entity = fs.entityForUri(toTestUri(name));
     if (data is String) {
       entity.writeAsStringSync(data);
     } else {
       entity.writeAsBytesSync(data);
     }
   });
   fs.entityForUri(toTestUri('.packages')).writeAsStringSync('');
-  fs
-      .entityForUri(invalidCoreLibsSpecUri)
-      .writeAsStringSync(_invalidLibrariesSpec);
   options
     ..verify = true
     ..fileSystem = new HybridFileSystem(fs)
     ..inputSummaries = inputSummaries.map(toTestUri).toList()
     ..linkedDependencies = linkedDependencies.map(toTestUri).toList()
     ..packagesFileUri = toTestUri('.packages');
 
   if (options.sdkSummary == null) {
     options.sdkRoot = await computePatchedSdk();
   }
 }
 
 /// A fake absolute directory used as the root of a memory-file system in the
 /// helpers above.
 Uri _defaultDir = Uri.parse('file:///a/b/c/');
 
 /// Convert relative file paths into an absolute Uri as expected by the test
 /// 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';
 
 /// Find a library in [program] whose Uri ends with the given [suffix]
 Library findLibrary(Program program, String suffix) {
   return program.libraries
       .firstWhere((lib) => lib.importUri.path.endsWith(suffix));
 }