Add tests

test/unit/dynamic-import.html

@@ -65,6 +65,40 @@
         }, null, true);
       });
 
+      test('importHref does not leak event listeners on load', function(done) {
+        var errorSpy = sinon.spy();
+        var loadSpy = sinon.spy(function(e) {
+          var target = e.target;
+          target.dispatchEvent(new Event('error'));
+          assert.isFalse(errorSpy.called, 'doesn\'t trigger the error event listener');
+          setTimeout(function() {
+            loadSpy.reset();
+            target.dispatchEvent(new Event('load'));
+            assert.isFalse(loadSpy.called, 'doesn\'t trigger the load event listener');
+            done();
+          });
+        });
+
+        Polymer.Base.importHref('dynamic-imports/async-import.html', loadSpy, errorSpy, true);
+      });
+
+      test('importHref does not leak event listeners on error', function(done) {
+        var loadSpy = sinon.spy();
+        var errorSpy = sinon.spy(function(e) {
+          var target = e.target;
+          target.dispatchEvent(new Event('load'));
+          assert.isFalse(loadSpy.called, 'doesn\'t trigger the load event listener');
+          setTimeout(function() {
+            errorSpy.reset();
+            target.dispatchEvent(new Event('error'));
+            assert.isFalse(errorSpy.called, 'doesn\'t trigger the error event listener');
+            done();
+          });
+        });
+
+        Polymer.Base.importHref('dynamic-imports/async-import-invalid.html', loadSpy, errorSpy, true);
+      });
+
     });
 
   });