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diff --git a/gfx/layers/ipc/CompositableForwarder.h b/gfx/layers/ipc/CompositableForwarder.h
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+++ b/gfx/layers/ipc/CompositableForwarder.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 MOZILLA_LAYERS_COMPOSITABLEFORWARDER
+#define MOZILLA_LAYERS_COMPOSITABLEFORWARDER
+
+#include <stdint.h>  // for int32_t, uint32_t, uint64_t
+#include "mozilla/Assertions.h"  // for AssertionConditionType, MOZ_ASSERT, MOZ_ASSERT_HELPER1
+#include "mozilla/Atomics.h"
+#include "mozilla/RefPtr.h"             // for RefPtr
+#include "mozilla/TimeStamp.h"          // for TimeStamp
+#include "mozilla/ipc/ProtocolUtils.h"  // for IToplevelProtocol, ProtocolID
+#include "mozilla/layers/KnowsCompositor.h"  // for KnowsCompositor
+#include "nsRect.h"                          // for nsIntRect
+#include "nsRegion.h"                        // for nsIntRegion
+#include "nsTArray.h"                        // for nsTArray
+
+namespace mozilla {
+namespace layers {
+class CompositableClient;
+class CompositableHandle;
+class ImageContainer;
+class PTextureChild;
+class SurfaceDescriptorTiles;
+class TextureClient;
+
+/**
+ * FwdTransactionCounter issues forwarder transaction numbers that represent a
+ * sequential stream of transactions to be transported over IPDL. Since every
+ * top-level protocol represents its own independently-sequenced IPDL queue,
+ * transaction numbers most naturally align with top-level protocols, rather
+ * than have different sub-protocols with their own independent transaction
+ * numbers that can't be usefully sequenced. FwdTransactionCounter expects
+ * users of it to provide themselves as proof they are a top-level protocol
+ * to avoid issues.
+ */
+struct FwdTransactionCounter {
+  explicit FwdTransactionCounter(mozilla::ipc::IToplevelProtocol* aToplevel)
+      : mFwdTransactionType(aToplevel->GetProtocolId()) {}
+
+  /**
+   * The ID of the top-level protocol. This is useful to tag the source of
+   * the transaction numbers in case different sources must be disambiguated.
+   */
+  mozilla::ipc::ProtocolId mFwdTransactionType;
+
+  /**
+   * Transaction id of ShadowLayerForwarder.
+   * It is incremented by UpdateFwdTransactionId() in each BeginTransaction()
+   * call.
+   */
+  uint64_t mFwdTransactionId = 0;
+};
+
+/**
+ * FwdTransactionTracker is to be used by CompositableForwarder consumers that
+ * must remember the last transaction in which they were used.
+ */
+class FwdTransactionTracker {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(FwdTransactionTracker)
+
+  static already_AddRefed<FwdTransactionTracker> GetOrCreate(
+      RefPtr<FwdTransactionTracker>& aTracker) {
+    if (!aTracker) {
+      aTracker = new FwdTransactionTracker;
+    }
+    return do_AddRef(aTracker);
+  }
+
+  bool IsUsed() const { return mFwdTransactionType && mFwdTransactionId; }
+
+  void Use(const FwdTransactionCounter& aCounter) {
+    mFwdTransactionType = aCounter.mFwdTransactionType;
+    mFwdTransactionId = aCounter.mFwdTransactionId;
+  }
+
+  Atomic<mozilla::ipc::ProtocolId> mFwdTransactionType{
+      (mozilla::ipc::ProtocolId)0};
+  Atomic<uint64_t> mFwdTransactionId{0};
+
+ private:
+  FwdTransactionTracker() = default;
+  ~FwdTransactionTracker() = default;
+};
+
+inline RemoteTextureTxnType ToRemoteTextureTxnType(
+    const RefPtr<FwdTransactionTracker>& aTracker) {
+  return aTracker ? (RemoteTextureTxnType)aTracker->mFwdTransactionType : 0;
+}
+
+inline RemoteTextureTxnId ToRemoteTextureTxnId(
+    const RefPtr<FwdTransactionTracker>& aTracker) {
+  return aTracker ? (RemoteTextureTxnId)aTracker->mFwdTransactionId : 0;
+}
+
+/**
+ * A transaction is a set of changes that happenned on the content side, that
+ * should be sent to the compositor side.
+ * CompositableForwarder is an interface to manage a transaction of
+ * compositable objetcs.
+ *
+ * ShadowLayerForwarder is an example of a CompositableForwarder (that can
+ * additionally forward modifications of the Layer tree).
+ * ImageBridgeChild is another CompositableForwarder.
+ *
+ * CompositableForwarder implements KnowsCompositor for simplicity as all
+ * implementations of CompositableForwarder currently also implement
+ * KnowsCompositor. This dependency could be split if we add new use cases.
+ */
+class CompositableForwarder : public KnowsCompositor {
+ public:
+  CompositableForwarder();
+  ~CompositableForwarder();
+
+  /**
+   * Setup the IPDL actor for aCompositable to be part of layers
+   * transactions.
+   */
+  virtual void Connect(CompositableClient* aCompositable,
+                       ImageContainer* aImageContainer = nullptr) = 0;
+
+  virtual void ReleaseCompositable(const CompositableHandle& aHandle) = 0;
+  virtual bool DestroyInTransaction(PTextureChild* aTexture) = 0;
+
+  /**
+   * Tell the CompositableHost on the compositor side to remove the texture
+   * from the CompositableHost.
+   * This function does not delete the TextureHost corresponding to the
+   * TextureClient passed in parameter.
+   * When the TextureClient has TEXTURE_DEALLOCATE_CLIENT flag,
+   * the transaction becomes synchronous.
+   */
+  virtual void RemoveTextureFromCompositable(CompositableClient* aCompositable,
+                                             TextureClient* aTexture) = 0;
+
+  struct TimedTextureClient {
+    TimedTextureClient()
+        : mTextureClient(nullptr), mFrameID(0), mProducerID(0) {}
+
+    TextureClient* mTextureClient;
+    TimeStamp mTimeStamp;
+    nsIntRect mPictureRect;
+    int32_t mFrameID;
+    int32_t mProducerID;
+  };
+  /**
+   * Tell the CompositableHost on the compositor side what textures to use for
+   * the next composition.
+   */
+  virtual void UseTextures(CompositableClient* aCompositable,
+                           const nsTArray<TimedTextureClient>& aTextures) = 0;
+
+  virtual void UseRemoteTexture(
+      CompositableClient* aCompositable, const RemoteTextureId aTextureId,
+      const RemoteTextureOwnerId aOwnerId, const gfx::IntSize aSize,
+      const TextureFlags aFlags,
+      const RefPtr<layers::FwdTransactionTracker>& aTracker) = 0;
+
+  void UpdateFwdTransactionId() {
+    ++GetFwdTransactionCounter().mFwdTransactionId;
+  }
+  uint64_t GetFwdTransactionId() {
+    return GetFwdTransactionCounter().mFwdTransactionId;
+  }
+  mozilla::ipc::ProtocolId GetFwdTransactionType() {
+    return GetFwdTransactionCounter().mFwdTransactionType;
+  }
+
+  virtual bool InForwarderThread() = 0;
+
+  void AssertInForwarderThread() { MOZ_ASSERT(InForwarderThread()); }
+
+ protected:
+  virtual FwdTransactionCounter& GetFwdTransactionCounter() = 0;
+
+  void TrackFwdTransaction(const RefPtr<FwdTransactionTracker>& aTracker) {
+    if (aTracker) {
+      aTracker->Use(GetFwdTransactionCounter());
+    }
+  }
+
+  nsTArray<RefPtr<TextureClient>> mTexturesToRemove;
+  nsTArray<RefPtr<CompositableClient>> mCompositableClientsToRemove;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif