Don't use `console` unconditionally (because of IE9).

pkg/browser/lib/interop.js

Index: pkg/browser/lib/interop.js
diff --git a/pkg/browser/lib/interop.js b/pkg/browser/lib/interop.js
index 91ca9de0a690866a82a6fc2e72d90e6d0b05e43c..ec02e5857ad195d2df1c15a768f83fda4b7fa098 100644
--- a/pkg/browser/lib/interop.js
+++ b/pkg/browser/lib/interop.js
@@ -3,5 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 // TODO(jmesserly): remove this script after a deprecation period.
-console.warn('<script src="packages/browser/interop.js"> is no longer ' +
-    'needed for dart:js. See http://pub.dartlang.org/packages/browser.');
+if (typeof console == "object" && typeof console.warn == "function") {
+  console.warn('<script src="packages/browser/interop.js"> is no longer ' +
+      'needed for dart:js. See http://pub.dartlang.org/packages/browser.');
+}