Add a Pub validator for READMEs that are invalid utf-8.

utils/tests/pub/test_pub.dart

Index: utils/tests/pub/test_pub.dart
diff --git a/utils/tests/pub/test_pub.dart b/utils/tests/pub/test_pub.dart
index 66d9434f2a373f364d9ce21ef98ed9ac5d0eb62a..abec9d4229008529dbadc7ce7f2e5238fdd5f951 100644
--- a/utils/tests/pub/test_pub.dart
+++ b/utils/tests/pub/test_pub.dart
@@ -14,6 +14,7 @@ import 'dart:io';
 import 'dart:json' as json;
 import 'dart:math';
 import 'dart:uri';
+import 'dart:utf';
 
 import '../../../pkg/http/lib/testing.dart';
 import '../../../pkg/oauth2/lib/oauth2.dart' as oauth2;
@@ -49,6 +50,10 @@ initConfig() {
 FileDescriptor file(Pattern name, String contents) =>
     new FileDescriptor(name, contents);
 
+/// Creates a new [FileDescriptor] with [name] and [contents].
+FileDescriptor binaryFile(Pattern name, List<int> contents) =>
+    new FileDescriptor.bytes(name, contents);
+
 /// Creates a new [DirectoryDescriptor] with [name] and [contents].
 DirectoryDescriptor dir(Pattern name, [List<Descriptor> contents]) =>
     new DirectoryDescriptor(name, contents);
@@ -866,16 +871,17 @@ abstract class Descriptor {
 /// tree before running a test, and for validating that the file system matches
 /// some expectations after running it.
 class FileDescriptor extends Descriptor {
-  /// The text contents of the file.
-  final String contents;
+  /// The contents of the file, in bytes.
+  final List<int> contents;
 
-  FileDescriptor(Pattern name, this.contents) : super(name);
+  FileDescriptor.bytes(Pattern name, this.contents) : super(name);
+
+  FileDescriptor(Pattern name, String contents) :
+      this.bytes(name, encodeUtf8(contents));
 
   /// Creates the file within [dir]. Returns a [Future] that is completed after
   /// the creation is done.
-  Future<File> create(dir) {
-    return writeTextFile(join(dir, _stringName), contents);
-  }
+  Future<File> create(dir) => writeByteFile(join(dir, _stringName), contents);
 
   /// Deletes the file within [dir]. Returns a [Future] that is completed after
   /// the deletion is done.