Fix some crashes.

pkg/front_end/lib/src/fasta/translate_uri.dart

 // Copyright (c) 2016, 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 fasta.translate_uri;
 
 import 'dart:async' show Future;
 
-import 'dart:io' show File;
+import 'package:package_config/packages_file.dart' as packages_file show parse;
 
-import 'package:package_config/packages_file.dart' as packages_file show parse;
+import 'errors.dart' show inputError;
+
+import 'io.dart' show readBytesFromFile;
+
+import 'scanner/characters.dart' show $LF;
 
 class TranslateUri {
   final Map<String, Uri> packages;
   final Map<String, Uri> dartLibraries;
 
   TranslateUri(this.packages, this.dartLibraries);
 
   Uri translate(Uri uri) {
     if (uri.scheme == "dart") return translateDartUri(uri);
     if (uri.scheme == "package") return translatePackageUri(uri);
@@ skipping 45 matching lines @@
         "web_gl": sdk.resolve("lib/web_gl/dartium/web_gl_dartium.dart"),
         "web_sql": sdk.resolve("lib/web_sql/dartium/web_sql_dartium.dart"),
         "_internal": sdk.resolve("lib/internal/internal.dart"),
         "profiler": sdk.resolve("lib/profiler/profiler.dart"),
         "vmservice_io": sdk.resolve("lib/vmservice_io/vmservice_io.dart"),
         "_vmservice": sdk.resolve("lib/vmservice/vmservice.dart"),
         "_builtin": sdk.resolve("lib/_builtin/_builtin.dart"),
       };
     }
     uri ??= Uri.base.resolve(".packages");
-    File file = new File.fromUri(uri);
-    List<int> bytes = await file.readAsBytes();
-    Map<String, Uri> packages = packages_file.parse(bytes, uri);
+    List<int> bytes = await readBytesFromFile(uri);
+    Map<String, Uri> packages = const <String, Uri>{};
+    try {
+      // We always add an extra zero byte at the end of files. We change that
+      // to a newline to avoid a format error from `packages_file.parse`.
+      bytes[bytes.length - 1] = $LF;
+      packages = packages_file.parse(bytes, uri);
+    } on FormatException catch (e) {
+      return inputError(uri, e.offset, e.message);
+    }
     return new TranslateUri(packages, dartLibraries);
   }
 }