Add a class-level comment on DOMWindow.

This CL has no behavior changes.

Change-Id: I11622b7dd02221b7a449a784284595a7edbab5c3
Reviewed-on: https://chromium-review.googlesource.com/c/1345691Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609939}

third_party/blink/renderer/core/frame/dom_window.h

@@ -28,6 +28,13 @@ class SerializedScriptValue;
 class WindowPostMessageOptions;
 class WindowProxyManager;
 
+// DOMWindow is an abstract class of Window interface implementations.
+// We have two derived implementation classes;  LocalDOMWindow and
+// RemoteDOMWindow.
+//
+// TODO(tkent): Rename DOMWindow to Window. The class was named as 'DOMWindow'
+// because WebKit already had KJS::Window.  We have no reasons to avoid
+// blink::Window now.
 class CORE_EXPORT DOMWindow : public EventTargetWithInlineData,
                               public DOMWindowBase64 {
   DEFINE_WRAPPERTYPEINFO();