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diff --git a/dom/animation/KeyframeUtils.h b/dom/animation/KeyframeUtils.h
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+++ b/dom/animation/KeyframeUtils.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_KeyframeUtils_h
+#define mozilla_KeyframeUtils_h
+
+#include "mozilla/KeyframeEffectParams.h"  // For CompositeOperation
+#include "nsCSSPropertyID.h"
+#include "nsTArrayForwardDeclare.h"  // For nsTArray
+#include "js/RootingAPI.h"           // For JS::Handle
+
+struct JSContext;
+class JSObject;
+
+namespace mozilla {
+struct AnimationProperty;
+class ComputedStyle;
+
+enum class PseudoStyleType : uint8_t;
+class ErrorResult;
+struct Keyframe;
+struct PropertyStyleAnimationValuePair;
+
+namespace dom {
+class Document;
+class Element;
+}  // namespace dom
+}  // namespace mozilla
+
+namespace mozilla {
+
+// Represents the set of property-value pairs on a Keyframe converted to
+// computed values.
+using ComputedKeyframeValues = nsTArray<PropertyStyleAnimationValuePair>;
+
+/**
+ * Utility methods for processing keyframes.
+ */
+class KeyframeUtils {
+ public:
+  /**
+   * Converts a JS value representing a property-indexed keyframe or a sequence
+   * of keyframes to an array of Keyframe objects.
+   *
+   * @param aCx The JSContext that corresponds to |aFrames|.
+   * @param aDocument The document to use when parsing CSS properties.
+   * @param aFrames The JS value, provided as an optional IDL |object?| value,
+   *   that is the keyframe list specification.
+   * @param aContext Information about who is trying to get keyframes from the
+   *   object, for use in error reporting.  This must be be a non-null
+   *   pointer representing a null-terminated ASCII string.
+   * @param aRv (out) Out-param to hold any error returned by this function.
+   *   Must be initially empty.
+   * @return The set of processed keyframes. If an error occurs, aRv will be
+   *   filled-in with the appropriate error code and an empty array will be
+   *   returned.
+   */
+  static nsTArray<Keyframe> GetKeyframesFromObject(
+      JSContext* aCx, dom::Document* aDocument, JS::Handle<JSObject*> aFrames,
+      const char* aContext, ErrorResult& aRv);
+
+  /**
+   * Calculate the computed offset of keyframes by evenly distributing keyframes
+   * with a missing offset.
+   *
+   * @see
+   * https://drafts.csswg.org/web-animations/#calculating-computed-keyframes
+   *
+   * @param aKeyframes The set of keyframes to adjust.
+   */
+  static void DistributeKeyframes(nsTArray<Keyframe>& aKeyframes);
+
+  /**
+   * Converts an array of Keyframe objects into an array of AnimationProperty
+   * objects. This involves creating an array of computed values for each
+   * longhand property and determining the offset and timing function to use
+   * for each value.
+   *
+   * @param aKeyframes The input keyframes.
+   * @param aElement The context element.
+   * @param aStyle The computed style values.
+   * @param aEffectComposite The composite operation specified on the effect.
+   *   For any keyframes in |aKeyframes| that do not specify a composite
+   *   operation, this value will be used.
+   * @return The set of animation properties. If an error occurs, the returned
+   *   array will be empty.
+   */
+  static nsTArray<AnimationProperty> GetAnimationPropertiesFromKeyframes(
+      const nsTArray<Keyframe>& aKeyframes, dom::Element* aElement,
+      PseudoStyleType aPseudoType, const ComputedStyle* aStyle,
+      dom::CompositeOperation aEffectComposite);
+
+  /**
+   * Check if the property or, for shorthands, one or more of
+   * its subproperties, is animatable.
+   *
+   * @param aProperty The property to check.
+   * @param aBackend  The style backend, Servo or Gecko, that should determine
+   *                  if the property is animatable or not.
+   * @return true if |aProperty| is animatable.
+   */
+  static bool IsAnimatableProperty(nsCSSPropertyID aProperty);
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_KeyframeUtils_h