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diff --git a/core/fxcrt/observable.h b/core/fxcrt/observable.h
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+++ b/core/fxcrt/observable.h
@@ -0,0 +1,87 @@
+// Copyright 2016 PDFium 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 CORE_FXCRT_OBSERVABLE_H_
+#define CORE_FXCRT_OBSERVABLE_H_
+
+#include <set>
+
+#include "core/fxcrt/fx_system.h"
+#include "third_party/base/stl_util.h"
+
+namespace fxcrt {
+
+template <class T>
+class Observable {
+ public:
+  class ObservedPtr {
+   public:
+    ObservedPtr() : m_pObservable(nullptr) {}
+    explicit ObservedPtr(T* pObservable) : m_pObservable(pObservable) {
+      if (m_pObservable)
+        m_pObservable->AddObservedPtr(this);
+    }
+    ObservedPtr(const ObservedPtr& that) : ObservedPtr(that.Get()) {}
+    ~ObservedPtr() {
+      if (m_pObservable)
+        m_pObservable->RemoveObservedPtr(this);
+    }
+    void Reset(T* pObservable = nullptr) {
+      if (m_pObservable)
+        m_pObservable->RemoveObservedPtr(this);
+      m_pObservable = pObservable;
+      if (m_pObservable)
+        m_pObservable->AddObservedPtr(this);
+    }
+    void OnDestroy() {
+      ASSERT(m_pObservable);
+      m_pObservable = nullptr;
+    }
+    ObservedPtr& operator=(const ObservedPtr& that) {
+      Reset(that.Get());
+      return *this;
+    }
+    bool operator==(const ObservedPtr& that) const {
+      return m_pObservable == that.m_pObservable;
+    }
+    bool operator!=(const ObservedPtr& that) const { return !(*this == that); }
+    explicit operator bool() const { return !!m_pObservable; }
+    T* Get() const { return m_pObservable; }
+    T& operator*() const { return *m_pObservable; }
+    T* operator->() const { return m_pObservable; }
+
+   private:
+    T* m_pObservable;
+  };
+
+  Observable() {}
+  Observable(const Observable& that) = delete;
+  ~Observable() { NotifyObservedPtrs(); }
+  void AddObservedPtr(ObservedPtr* pObservedPtr) {
+    ASSERT(!pdfium::ContainsKey(m_ObservedPtrs, pObservedPtr));
+    m_ObservedPtrs.insert(pObservedPtr);
+  }
+  void RemoveObservedPtr(ObservedPtr* pObservedPtr) {
+    ASSERT(pdfium::ContainsKey(m_ObservedPtrs, pObservedPtr));
+    m_ObservedPtrs.erase(pObservedPtr);
+  }
+  void NotifyObservedPtrs() {
+    for (auto* pObservedPtr : m_ObservedPtrs)
+      pObservedPtr->OnDestroy();
+    m_ObservedPtrs.clear();
+  }
+  Observable& operator=(const Observable& that) = delete;
+
+ protected:
+  size_t ActiveObservedPtrsForTesting() const { return m_ObservedPtrs.size(); }
+
+ private:
+  std::set<ObservedPtr*> m_ObservedPtrs;
+};
+
+}  // namespace fxcrt
+
+using fxcrt::Observable;
+
+#endif  // CORE_FXCRT_OBSERVABLE_H_