Added top level definition to Window.

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index f7c0641f6433524f4eb4b6192b1549e49e324ad7..d76729fd150bce9409fe4de40681689a63fef0b0 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -28466,6 +28466,22 @@ class _XSLTProcessorFactoryProvider {
 // BSD-style license that can be found in the LICENSE file.
 
 
+/**
+ * An object representing the top-level context object for web scripting.
+ *
+ * In a web browser, a [Window] object represents the actual browser window.
+ * In a multi-tabbed browser, each tab has its own [Window] object. A [Window]
+ * is the container that displays a [Document]'s content. All web scripting
+ * happens within the context of a [Window] object.
+ *
+ * **Note:** This class represents any window, whereas [LocalWindow] is
+ * used to access the properties and content of the current window.
+ *
+ * See also:
+ *
+ * * [DOM Window](https://developer.mozilla.org/en-US/docs/DOM/window) from MDN.
+ * * [Window](http://www.w3.org/TR/Window/) from the W3C.
+ */
 abstract class Window {
   // Fields.
   Location get location;