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diff --git a/gfx/angle/checkout/src/libANGLE/Observer.cpp b/gfx/angle/checkout/src/libANGLE/Observer.cpp
new file mode 100644
index 0000000000..75f51648a4
--- /dev/null
+++ b/gfx/angle/checkout/src/libANGLE/Observer.cpp
@@ -0,0 +1,113 @@
+//
+// Copyright 2018 The ANGLE Project Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Observer:
+//   Implements the Observer pattern for sending state change notifications
+//   from Subject objects to dependent Observer objects.
+//
+//   See design document:
+//   https://docs.google.com/document/d/15Edfotqg6_l1skTEL8ADQudF_oIdNa7i8Po43k6jMd4/
+
+#include "libANGLE/Observer.h"
+
+#include <algorithm>
+
+#include "common/debug.h"
+
+namespace angle
+{
+namespace
+{}  // anonymous namespace
+
+// Observer implementation.
+ObserverInterface::~ObserverInterface() = default;
+
+// Subject implementation.
+Subject::Subject() {}
+
+Subject::~Subject()
+{
+    resetObservers();
+}
+
+bool Subject::hasObservers() const
+{
+    return !mObservers.empty();
+}
+
+void Subject::onStateChange(SubjectMessage message) const
+{
+    if (mObservers.empty())
+        return;
+
+    for (const ObserverBindingBase *binding : mObservers)
+    {
+        binding->getObserver()->onSubjectStateChange(binding->getSubjectIndex(), message);
+    }
+}
+
+void Subject::resetObservers()
+{
+    for (angle::ObserverBindingBase *binding : mObservers)
+    {
+        binding->onSubjectReset();
+    }
+    mObservers.clear();
+}
+
+// ObserverBinding implementation.
+ObserverBinding::ObserverBinding() : ObserverBindingBase(nullptr, 0), mSubject(nullptr) {}
+
+ObserverBinding::ObserverBinding(ObserverInterface *observer, SubjectIndex index)
+    : ObserverBindingBase(observer, index), mSubject(nullptr)
+{
+    ASSERT(observer);
+}
+
+ObserverBinding::~ObserverBinding()
+{
+    reset();
+}
+
+ObserverBinding::ObserverBinding(const ObserverBinding &other)
+    : ObserverBindingBase(other), mSubject(nullptr)
+{
+    bind(other.mSubject);
+}
+
+ObserverBinding &ObserverBinding::operator=(const ObserverBinding &other)
+{
+    reset();
+    ObserverBindingBase::operator=(other);
+    bind(other.mSubject);
+    return *this;
+}
+
+void ObserverBinding::bind(Subject *subject)
+{
+    ASSERT(getObserver() || !subject);
+    if (mSubject)
+    {
+        mSubject->removeObserver(this);
+    }
+
+    mSubject = subject;
+
+    if (mSubject)
+    {
+        mSubject->addObserver(this);
+    }
+}
+
+void ObserverBinding::onStateChange(SubjectMessage message) const
+{
+    getObserver()->onSubjectStateChange(getSubjectIndex(), message);
+}
+
+void ObserverBinding::onSubjectReset()
+{
+    mSubject = nullptr;
+}
+}  // namespace angle