WIP - Rough draft of style observation in style of apply hooks.

Source/core/style/StyleObserver.cpp

Index: Source/core/style/StyleObserver.cpp
diff --git a/Source/modules/mediasession/MediaSession.cpp b/Source/core/style/StyleObserver.cpp
similarity index 50%
copy from Source/modules/mediasession/MediaSession.cpp
copy to Source/core/style/StyleObserver.cpp
index 937bf7f19d23f26aadf5c3f1ae0393ae0050d093..657e715586be3003e314707928cd2aa0b928ee87 100644
--- a/Source/modules/mediasession/MediaSession.cpp
+++ b/Source/core/style/StyleObserver.cpp
@@ -1,23 +1,18 @@
 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-
 #include "config.h"
-#include "modules/mediasession/MediaSession.h"
+#include "core/style/StyleObserver.h"
 
 namespace blink {
 
-MediaSession* MediaSession::create()
-{
-    return new MediaSession;
-}
+StyleObserver::StyleObserver() : m_weakPtrFactory(this) {}
 
-void MediaSession::activate()
-{
-}
+StyleObserver::~StyleObserver() {}
 
-void MediaSession::deactivate()
+WeakPtr<StyleObserver> StyleObserver::createWeakPtr()
 {
+    return m_weakPtrFactory.createWeakPtr();
 }
 
 } // namespace blink