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diff --git a/gfx/src/CompositorHitTestInfo.h b/gfx/src/CompositorHitTestInfo.h
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+++ b/gfx/src/CompositorHitTestInfo.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_GFX_COMPOSITORHITTESTINFO_H_
+#define MOZILLA_GFX_COMPOSITORHITTESTINFO_H_
+
+#include "mozilla/EnumSet.h"
+#include "mozilla/EnumTypeTraits.h"
+
+namespace mozilla {
+namespace gfx {
+
+// This set of flags is used to figure out what information a frame has
+// that is relevant to hit-testing in the compositor. The flags are
+// intentionally set up so that if all of them are 0 the item is effectively
+// invisible to hit-testing, and no information for this frame needs to be
+// sent to the compositor.
+// Each enumerator is annotated with the value it contributes to an
+// EnumSet (2 ^ <value of enumerator>), in hexadecimal.
+enum class CompositorHitTestFlags : uint8_t {
+  // The frame participates in hit-testing
+  eVisibleToHitTest = 0,  // 0x0001
+
+  // The frame may have odd shapes that requires the main thread to do accurate
+  // hit-testing.
+  eIrregularArea,  // 0x0002
+  // The frame has APZ-aware listeners and so inputs targeted at this area
+  // need to be handled by the main thread before APZ can use them, as they
+  // might be prevent-defaulted.
+  eApzAwareListeners,  // 0x0004
+  // This is an inactive scrollframe or unlayerized scrollthumb. In this state
+  // it cannot be used by APZ for async scrolling, so APZ will defer to the main
+  // thread.
+  eInactiveScrollframe,  // 0x0008
+
+  // The touch action flags are set up so that the default of
+  // touch-action:auto on an element leaves all the flags as 0.
+  eTouchActionPanXDisabled,           // 0x0010
+  eTouchActionPanYDisabled,           // 0x0020
+  eTouchActionPinchZoomDisabled,      // 0x0040
+  eTouchActionAnimatingZoomDisabled,  // 0x0080
+
+  // The frame is a scrollbar or a subframe inside a scrollbar (including
+  // scroll thumbs)
+  eScrollbar,  // 0x0100
+  // The frame is a scrollthumb. If this is set then eScrollbar will also be
+  // set, unless gecko somehow generates a scroll thumb without a containing
+  // scrollbar.
+  eScrollbarThumb,  // 0x0200
+  // If eScrollbar is set, this flag indicates if the scrollbar is a vertical
+  // one (if set) or a horizontal one (if not set)
+  eScrollbarVertical,  // 0x0400
+
+  // Events targeting this frame should only be processed if a target
+  // confirmation is received from the main thread. If no such confirmation
+  // is received within a timeout period, the event may be dropped.
+  // Only meaningful in combination with eDispatchToContent.
+  eRequiresTargetConfirmation,  // 0x0800
+
+  // Bits 0x1000, 0x2000, 0x4000, and 0x8000 are used by SideBitsPacked in
+  // WebRenderAPI.cpp when we pack SideBits and CompositorHitTestInfo into a
+  // uint16_t and pass in into webrender to store in the item tag.
+
+};
+
+using CompositorHitTestInfo = EnumSet<CompositorHitTestFlags, uint32_t>;
+
+// A CompositorHitTestInfo with none of the flags set
+constexpr CompositorHitTestInfo CompositorHitTestInvisibleToHit;
+
+// Mask to check for all the touch-action flags at once
+constexpr CompositorHitTestInfo CompositorHitTestTouchActionMask(
+    CompositorHitTestFlags::eTouchActionPanXDisabled,
+    CompositorHitTestFlags::eTouchActionPanYDisabled,
+    CompositorHitTestFlags::eTouchActionPinchZoomDisabled,
+    CompositorHitTestFlags::eTouchActionAnimatingZoomDisabled);
+
+// Mask to check all the flags that involve APZ waiting for results from the
+// main thread
+constexpr CompositorHitTestInfo CompositorHitTestDispatchToContent(
+    CompositorHitTestFlags::eIrregularArea,
+    CompositorHitTestFlags::eApzAwareListeners,
+    CompositorHitTestFlags::eInactiveScrollframe);
+
+}  // namespace gfx
+
+// Used for IPDL serialization. The 'value' have to be the biggest enum from
+// CompositorHitTestFlags.
+template <>
+struct MaxEnumValue<::mozilla::gfx::CompositorHitTestFlags> {
+  static constexpr unsigned int value = static_cast<unsigned int>(
+      gfx::CompositorHitTestFlags::eRequiresTargetConfirmation);
+};
+
+namespace gfx {
+
+// Checks if the CompositorHitTestFlags max enum value is less than N.
+template <int N>
+static constexpr bool DoesCompositorHitTestInfoFitIntoBits() {
+  if (MaxEnumValue<CompositorHitTestInfo::valueType>::value < N) {
+    return true;
+  }
+
+  return false;
+}
+}  // namespace gfx
+
+}  // namespace mozilla
+
+#endif /* MOZILLA_GFX_COMPOSITORHITTESTINFO_H_ */