fix dart2js warnings in polymer_expressions pkg

pkg/polymer_expressions/lib/src/globals.dart

Index: pkg/polymer_expressions/lib/src/globals.dart
diff --git a/pkg/polymer_expressions/lib/src/globals.dart b/pkg/polymer_expressions/lib/src/globals.dart
index 86a19d8522a87468e82c88f2da47d1d5a5777ad2..b51aeb3adbfc53e78ac112757e7cf0bacfb246b8 100644
--- a/pkg/polymer_expressions/lib/src/globals.dart
+++ b/pkg/polymer_expressions/lib/src/globals.dart
@@ -26,7 +26,6 @@ class IndexedValue<V> {
   IndexedValue(this.index, this.value);
 }
 
-
 /**
  * An [Iterable] of [IndexedValue]s where the nth value holds the nth
  * element of [iterable] and its index. See [enumerate].
@@ -37,7 +36,8 @@ class EnumerateIterable<V> extends IterableBase<IndexedValue<V>> {
 
   EnumerateIterable(this._iterable);
 
-  Iterator<V> get iterator => new EnumerateIterator<V>(_iterable.iterator);
+  Iterator<IndexedValue<V>> get iterator =>
+      new EnumerateIterator<V>(_iterable.iterator);
 
   // Length related functions are independent of the mapping.
   int get length => _iterable.length;
@@ -53,7 +53,7 @@ class EnumerateIterable<V> extends IterableBase<IndexedValue<V>> {
 
 /** The [Iterator] returned by [EnumerateIterable.iterator]. */
 class EnumerateIterator<V> extends Iterator<IndexedValue<V>> {
-  final Iterator<IndexedValue<V>> _iterator;
+  final Iterator<V> _iterator;
   int _index = 0;
   IndexedValue<V> _current;