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diff --git a/gfx/layers/TransactionIdAllocator.h b/gfx/layers/TransactionIdAllocator.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef GFX_TRANSACTION_ID_ALLOCATOR_H
+#define GFX_TRANSACTION_ID_ALLOCATOR_H
+
+#include "nsISupportsImpl.h"
+#include "mozilla/layers/LayersTypes.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/VsyncDispatcher.h"
+
+namespace mozilla {
+namespace layers {
+
+class TransactionIdAllocator {
+ protected:
+  virtual ~TransactionIdAllocator() = default;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING(TransactionIdAllocator)
+
+  /**
+   * Allocate a unique id number for the current refresh tick, can
+   * only be called while IsInRefresh().
+   *
+   * If too many id's are allocated without being returned then
+   * the refresh driver will suspend until they catch up. This
+   * "throttling" behaviour can be skipped by passing aThrottle=false.
+   * Otherwise call sites should generally be passing aThrottle=true.
+   */
+  virtual TransactionId GetTransactionId(bool aThrottle) = 0;
+
+  /**
+   * Return the transaction id that for the last non-revoked transaction.
+   * This allows the caller to tell whether a composite was triggered by
+   * a paint that occurred after a call to TransactionId().
+   */
+  virtual TransactionId LastTransactionId() const = 0;
+
+  /**
+   * Notify that all work (including asynchronous composites)
+   * for a given transaction id has been completed.
+   *
+   * If the refresh driver has been suspended because
+   * of having too many outstanding id's, then this may
+   * resume it.
+   */
+  virtual void NotifyTransactionCompleted(TransactionId aTransactionId) = 0;
+
+  /**
+   * Revoke a transaction id that isn't needed to track
+   * completion of asynchronous work. This is similar
+   * to NotifyTransactionCompleted except avoids
+   * return ordering issues.
+   */
+  virtual void RevokeTransactionId(TransactionId aTransactionId) = 0;
+
+  /**
+   * Stop waiting for pending transactions, if any.
+   *
+   * This is used when ClientLayerManager is assigning to another refresh
+   * driver, and the current refresh driver may never receive transaction
+   * completed notifications.
+   */
+  virtual void ClearPendingTransactions() = 0;
+
+  /**
+   * Transaction id is usually initialized as 0, however when ClientLayerManager
+   * switches to another refresh driver, completed transactions of the previous
+   * refresh driver could be delivered and confuse the newly adopted refresh
+   * driver. To prevent this situation, use this function to reset transaction
+   * id to the last transaction id from previous refresh driver, so that all
+   * completed transactions of previous refresh driver will be ignored.
+   */
+  virtual void ResetInitialTransactionId(TransactionId aTransactionId) = 0;
+
+  /**
+   * Get the start time of the current refresh tick.
+   */
+  virtual mozilla::TimeStamp GetTransactionStart() = 0;
+
+  virtual VsyncId GetVsyncId() = 0;
+
+  virtual mozilla::TimeStamp GetVsyncStart() = 0;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* GFX_TRANSACTION_ID_ALLOCATOR_H */