Refactor of PolymerExpressions. Adds "as" expressions.

pkg/polymer_expressions/test/eval_test.dart

Index: pkg/polymer_expressions/test/eval_test.dart
diff --git a/pkg/polymer_expressions/test/eval_test.dart b/pkg/polymer_expressions/test/eval_test.dart
index 2181215eb887734966d55aa0c17e4ef764e5d916..213f17ba48deeeee732ade8a155f446cd9b43ec3 100644
--- a/pkg/polymer_expressions/test/eval_test.dart
+++ b/pkg/polymer_expressions/test/eval_test.dart
@@ -216,24 +216,8 @@ main() {
       expectEval('a || b', false, null, {'a': null, 'b': null});
     });
 
-    test('should evaluate an "in" expression', () {
-      var scope = new Scope(variables: {'items': [1, 2, 3]});
-      var comprehension = eval(parse('item in items'), scope);
-      expect(comprehension.iterable, orderedEquals([1, 2, 3]));
-    });
-
-    test('should evaluate complex "in" expressions', () {
-      var holder = new ListHolder([1, 2, 3]);
-      var scope = new Scope(variables: {'holder': holder});
-      var comprehension = eval(parse('item in holder.items'), scope);
-      expect(comprehension.iterable, orderedEquals([1, 2, 3]));
-    });
-
-    test('should handle null iterators in "in" expressions', () {
-      var scope = new Scope(variables: {'items': null});
-      var comprehension = eval(parse('item in items'), scope);
-      expect(comprehension, isNotNull);
-      expect(comprehension.iterable, []);
+    test('should not evaluate "in" expressions', () {
+      expect(() => eval(parse('item in items'), null), throws);
     });
 
   });
@@ -340,19 +324,6 @@ main() {
       );
     });
 
-    test('should observe an comprehension', () {
-      var items = new ObservableList();
-      var foo = new Foo(name: 'foo');
-      return expectObserve('item in items',
-          variables: {'items': items},
-          beforeMatcher: (c) => c.iterable.isEmpty,
-          mutate: () {
-            items.add(foo);
-          },
-          afterMatcher: (c) => c.iterable.contains(foo)
-      );
-    });
-
   });
 
 }