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diff --git a/layout/style/MediaFeatureChange.h b/layout/style/MediaFeatureChange.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/. */
+
+/* A struct defining a media feature change. */
+
+#ifndef mozilla_MediaFeatureChange_h__
+#define mozilla_MediaFeatureChange_h__
+
+#include "nsChangeHint.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/TypedEnumBits.h"
+#include "mozilla/ServoStyleConsts.h"
+
+namespace mozilla {
+
+enum class MediaFeatureChangeReason : uint16_t {
+  // The viewport size the document has used has changed.
+  //
+  // This affects size media queries like min-width.
+  ViewportChange = 1 << 0,
+  // The effective text zoom has changed. This affects the meaning of em units,
+  // and thus affects any media query that uses a Length.
+  ZoomChange = 1 << 1,
+  // The resolution has changed. This can affect device-pixel-ratio media
+  // queries, for example.
+  ResolutionChange = 1 << 2,
+  // The medium has changed.
+  MediumChange = 1 << 3,
+  // The size-mode has changed.
+  SizeModeChange = 1 << 4,
+  // A system metric or multiple have changed. This affects all the media
+  // features that expose the presence of a system metric directly.
+  SystemMetricsChange = 1 << 5,
+  // The fact of whether the device size is the page size has changed, thus
+  // resolution media queries can change.
+  DeviceSizeIsPageSizeChange = 1 << 6,
+  // display-mode changed on the document, thus the display-mode media queries
+  // may have changed.
+  DisplayModeChange = 1 << 7,
+  // A preference that affects media query results has changed. For
+  // example, changes to document_color_use will affect
+  // prefers-contrast.
+  PreferenceChange = 1 << 8,
+};
+
+MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(MediaFeatureChangeReason)
+
+enum class MediaFeatureChangePropagation : uint8_t {
+  JustThisDocument = 0,
+  SubDocuments = 1 << 0,
+  Images = 1 << 1,
+  All = Images | SubDocuments,
+};
+
+MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(MediaFeatureChangePropagation)
+
+struct MediaFeatureChange {
+  static const auto kAllChanges = static_cast<MediaFeatureChangeReason>(~0);
+
+  RestyleHint mRestyleHint;
+  nsChangeHint mChangeHint;
+  MediaFeatureChangeReason mReason;
+
+  MOZ_IMPLICIT MediaFeatureChange(MediaFeatureChangeReason aReason)
+      : MediaFeatureChange(RestyleHint{0}, nsChangeHint(0), aReason) {}
+
+  MediaFeatureChange(RestyleHint aRestyleHint, nsChangeHint aChangeHint,
+                     MediaFeatureChangeReason aReason)
+      : mRestyleHint(aRestyleHint),
+        mChangeHint(aChangeHint),
+        mReason(aReason) {}
+
+  inline MediaFeatureChange& operator|=(const MediaFeatureChange& aOther) {
+    mRestyleHint |= aOther.mRestyleHint;
+    mChangeHint |= aOther.mChangeHint;
+    mReason |= aOther.mReason;
+    return *this;
+  }
+
+  static MediaFeatureChange ForPreferredColorSchemeChange() {
+    // We need to restyle because not only media queries have changed, system
+    // colors may as well via the prefers-color-scheme meta tag / effective
+    // color-scheme property value.
+    return {RestyleHint::RecascadeSubtree(), nsChangeHint(0),
+            MediaFeatureChangeReason::SystemMetricsChange};
+  }
+};
+
+}  // namespace mozilla
+
+#endif