Intersection Observer first draft

Source/core/dom/IntersectionObserver.idl

+// 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.
+
+// http://w3c.github.io/performance-timeline/#idl-def-PerformanceObserverCallback
+callback IntersectionObserverCallback = void (sequence <IntersectionObserverEntry> entries, IntersectionObserver observer);
+
+// https://
+[
+    CustomConstructor(IntersectionObserverCallback callback),
+    RuntimeEnabled=IntersectionObserver,
+    WillBeGarbageCollected,
+] interface IntersectionObserver {
+    [RaisesException] void observe(Element target, IntersectionObserverInit options);
+    void disconnect();
+    sequence <IntersectionObserverEntry> takeRecords();
+};