Fix some crashes.

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

Index: pkg/front_end/lib/src/fasta/translate_uri.dart
diff --git a/pkg/front_end/lib/src/fasta/translate_uri.dart b/pkg/front_end/lib/src/fasta/translate_uri.dart
index 429a65730bc11d336800761c5dadcf4f1fce79d7..37d98eeb3ca6998dac354f03a84c42f346f82848 100644
--- a/pkg/front_end/lib/src/fasta/translate_uri.dart
+++ b/pkg/front_end/lib/src/fasta/translate_uri.dart
@@ -6,10 +6,14 @@ 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 '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;
@@ -74,9 +78,16 @@ class TranslateUri {
       };
     }
     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);
   }
 }