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

utils/pub/package.dart

Index: utils/pub/package.dart
diff --git a/utils/pub/package.dart b/utils/pub/package.dart
index f62e2becd0ffbda4ff69ee4a14c900e1a78a3cde..15fcb97b65874279b40ab650285091dcb6ba299e 100644
--- a/utils/pub/package.dart
+++ b/utils/pub/package.dart
@@ -11,6 +11,8 @@ import 'source.dart';
 import 'source_registry.dart';
 import 'version.dart';
 
+final _README_REGEXP = new RegExp(r"^README($|\.)", caseSensitive: false);
+
 /// A named, versioned, unit of code and resource reuse.
 class Package {
   /// Loads the package whose root directory is [packageDir]. [name] is the
@@ -58,6 +60,26 @@ class Package {
   /// specified in the pubspec when this package depends on another.
   Collection<PackageRef> get dependencies => pubspec.dependencies;
 
+  /// Returns the path to the README file at the root of the entrypoint, or null
+  /// if no README file is found. If multiple READMEs are found, this uses the
+  /// same conventions as pub.dartlang.org for choosing the primary one: the
+  /// README with the fewest extensions that is lexically ordered first is
+  /// chosen.
+  Future<String> get readmePath {
+    return listDir(dir).then((entries) {
+      var readmes = entries.where((entry) => entry.contains(_README_REGEXP));
+      if (readmes.isEmpty) return;
+
+      return readmes.min((readme1, readme2) {
+        var extensions1 = ".".allMatches(readme1).length;
+        var extensions2 = ".".allMatches(readme2).length;
+        var comparison = extensions1.compareTo(extensions2);
+        if (comparison != 0) return comparison;
+        return readme1.compareTo(readme2);
+      });
+    });
+  }
+
   /// Constructs a package with the given pubspec. The package will have no
   /// directory associated with it.
   Package.inMemory(this.pubspec)