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diff --git a/image/PlaybackType.h b/image/PlaybackType.h
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+++ b/image/PlaybackType.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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_image_PlaybackType_h
+#define mozilla_image_PlaybackType_h
+
+#include "imgIContainer.h"
+
+namespace mozilla {
+namespace image {
+
+/**
+ * PlaybackType identifies a surface cache entry as either a static surface or
+ * an animation. Note that a specific cache entry is one or the other, but
+ * images may be associated with both types of cache entries, since in some
+ * circumstances we may want to treat an animated image as if it were static.
+ */
+enum class PlaybackType : uint8_t {
+  eStatic,   // Calls to DrawableRef() will always return the same surface.
+  eAnimated  // An animation; calls to DrawableRef() may return different
+             // surfaces at different times.
+};
+
+/**
+ * Given an imgIContainer FRAME_* value, returns the corresponding PlaybackType
+ * for use in surface cache lookups.
+ */
+inline PlaybackType ToPlaybackType(uint32_t aWhichFrame) {
+  MOZ_ASSERT(aWhichFrame == imgIContainer::FRAME_FIRST ||
+             aWhichFrame == imgIContainer::FRAME_CURRENT);
+  return aWhichFrame == imgIContainer::FRAME_CURRENT ? PlaybackType::eAnimated
+                                                     : PlaybackType::eStatic;
+}
+
+}  // namespace image
+}  // namespace mozilla
+
+#endif  // mozilla_image_PlaybackType_h