Adding IE support to browser prefixes.

lib/html/src/Device.dart

Index: lib/html/src/Device.dart
diff --git a/lib/html/src/Device.dart b/lib/html/src/Device.dart
index 7d8d54e17b3606ada5ed24435e9096acfc21e915..3dc6649fe9b6cf6fc4ce80e1e75d84e2f21a4846 100644
--- a/lib/html/src/Device.dart
+++ b/lib/html/src/Device.dart
@@ -14,6 +14,16 @@ class _Device {
   static String get userAgent() => window.navigator.userAgent;
 
   /**
+   * Determines if the current device is running Opera.
+   */
+  static bool get isOpera() => userAgent.contains("Opera", 0);
+
+  /**
+   * Determines if the current device is running Internet Explorer.
+   */
+  static bool get isIE() => !isOpera && userAgent.contains("MSIE", 0);
+
+  /**
    * Determines if the current device is running Firefox.
    */
   static bool get isFirefox() => userAgent.contains("Firefox", 0);