Fixing up WheelEvent to follow W3C standards and work on all platforms.

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 ecfc86008e4609791b2d1ec6bf5a7fa2a6361425..bc7976f9a49e64ccb893d0bd71c9ef4fa2c0c42f 100644
--- a/lib/html/src/Device.dart
+++ b/lib/html/src/Device.dart
@@ -27,4 +27,9 @@ class _Device {
    * Determines if the current device is running Firefox.
    */
   static bool get isFirefox => userAgent.contains("Firefox", 0);
+
+  /**
+   * Determines if the current device is running WebKit.
+   */
+  static bool get isWebKit => !isOpera && userAgent.contains("WebKit", 0);
 }