ResizeObserver pt5: size change notification

third_party/WebKit/Source/core/observer/ResizeObserverController.h

 // Copyright 2016 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.
 
 #ifndef ResizeObserverController_h
 #define ResizeObserverController_h
 
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class ResizeObserver;
 
 // ResizeObserverController keeps track of all ResizeObservers
 // in a single Document.
+//
+// The observation API is used to integrate ResizeObserver
+// and the event loop. It delivers notification in a loop.
+// In each iteration, only notifications deeper than the
+// shallowest notification from previous iteration are delivered.
 class ResizeObserverController final : public GarbageCollected<ResizeObserverController> {
 public:
+    static const size_t kDepthBottom = 4096;
+
     ResizeObserverController();
 
     void addObserver(ResizeObserver&);
 
+    // observation API
+    // Returns depth of shallowest observed node, kDepthLimit if none.
+    size_t gatherObservations(size_t deeperThan);
+    // Returns true if gatherObservations has skipped observations
+    // because they were too shallow.
+    bool skippedObservations();
+    void deliverObservations();
+    void clearObservations();
+    void observerChanged()  { m_observersChanged = true; }
+
     DECLARE_TRACE();
 
 private:
     // Active observers
     HeapHashSet<WeakMember<ResizeObserver>> m_observers;
+    // True if any observers were changed since last notification.
+    bool m_observersChanged;
 };
 
 } // namespace blink
 
 #endif